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In continuation with Paper I [S. R. Reddy et al., J. Chem. Phys. 151, 054303 (2019)], the vibronic structure and dynamics of the 1 Σ u + electronic state of C15, C17, C19, and C21 chains in the coupled manifold of 1 Σ u + –1Πg–1Πu– 1 Σ g + electronic states have been investigated in this paper. The model vibronic Hamiltonian developed through extensive ab initio quantum chemistry calculations in Paper I is employed, and first principles nuclear dynamics calculations are carried out to obtain the photoabsorption band of the 1 Σ u + electronic state. Both time-independent and time-dependent quantum mechanical calculations are carried out to precisely locate the vibrational levels, assign them with the progression of vibrational modes, and elucidate the impact of both Renner-Teller and pseudo-Renner-Teller couplings on them. The nonradiative decay of the 1 Σ u + electronic state is studied, and it is found that the decay rate is comparable with the prediction made for them to be qualified as a carrier of diffuse interstellar bands in the literature. The theoretical results are found to be in good accord with the available experimental results. [ABSTRACT FROM AUTHOR]

In a recent paper [Aschi et al., ChemPhysChem 6, 53 (2005)], we characterized, by means of theoretical-computational procedures, the electronic excitation of water along the typical liquid state isochore (55.32 mol/l) for a large range of temperature. In that paper we were able to accurately reproduce the experimental absorption maximum at room temperature and to provide a detailed description of the temperature dependence of the excitation spectrum along the isochore. In a recent experimental work by Marin et al. [J. Chem. Phys. 125, 104314 (2006)], water electronic excitation energy was carefully analyzed in a broad range of density and temperature, finding a remarkable agreement of the temperature behavior of the experimental data with our theoretical results. Here, by means of the same theoretical-computational procedures (molecular dynamics simulations and the perturbed matrix method), we investigate water electronic absorption exactly in the same density-temperature range used in the experimental work, hence, now considering also the absorption density dependence. Our results point out that, (1) for all the densities and temperatures investigated, our calculated absorption spectra are in very good agreement with the experimental ones and (2) the gradual maxima redshift observed increasing the temperature or decreasing the density has to be ascribed to a real shift of the lowest X→A electronic transition, supporting the conclusions of Marin et al. [ABSTRACT FROM AUTHOR]

Computational analysis of difference spectra between two analogous systems is a challenging issue, as reliable estimation of a tiny difference spectrum requires an extraordinary precision of the two original spectra. We have developed an alternative new method to calculate the difference spectra under background-free conditions, which greatly improved the efficiency of computation. In this paper, we report further improvement by using efficient parallel implementation and the time correlation formula based on time derivative quantities. As a consequence, the present work achieved further remarkable acceleration in the calculations of difference infrared and Raman spectra in the order of magnitude and thereby allowed us by analyzing these difference spectra at a practical cost of computation. [ABSTRACT FROM AUTHOR]

In this paper, a novel methodology is presented for the construction of ab initio effective rotation–vibration spectroscopic models from potential energy and dipole moment surfaces. Non-empirical effective Hamiltonians are obtained via the block-diagonalization of selected variationally computed eigenvector matrices. For the first time, the derivation of an effective dipole moment is carried out in a systematic way. This general approach can be implemented quite easily in most of the variational computer codes and turns out to be a clear alternative to the rather involved Van Vleck perturbation method. Symmetry is exploited at all stages to translate first-principles calculations into a set of spectroscopic parameters to be further refined on experiment. We demonstrate on H2CO, PH3, CH4, C2H4, and SF6 that the proposed effective model can provide crucial information to spectroscopists within a very short time compared to empirical spectroscopic models. This approach brings a new insight into high-resolution spectrum analysis of polyatomic molecules and will be also of great help in the modeling of hot atmospheres where completeness is important. [ABSTRACT FROM AUTHOR]

With the Hamiltonian derived in the preceding paper and the ab initio potentials of T. Bürgi, S. Graf, S. Leutwyler, and W. Klopper [J. Chem. Phys. 103, 1077 (1995)] and of J. G. C. M. van Duijneveldt-van de Rijdt and F. B. van Duijneveldt [Chem. Phys. Lett. 237, 560 (1995)], we calculate the pseudo-rotation tunneling levels in a rotating water trimer. The internal motions are treated by a three-dimensional discrete variable representation and the Coriolis coupling with the overall rotation is included. Also the effects of donor tunneling are included, by introducing semi-empirical coupling matrix elements. New experimental data are presented for the c-type band at 87.1 cm-1 in (H2O)3, which show that specific levels in the donor tunneling quartets of this band are further split into doublets. With the results of our quantitative calculations and the model of the preceding paper we can understand the mechanisms of all the splittings observed in the earlier high-resolution spectra of (H2O)3 and (D2O)3, as well as these new splittings, in terms of pseudo-rotation tunneling, donor tunneling and Coriolis coupling. An unambiguous assignment is given of all the bands observed and analyzed. The ab initio potential of the Van Duijneveldts yields accurate energies of the lower pseudo-rotation levels, the potential of Bürgi et al. performs better for the higher levels. With our analysis we can deduce from the spectra that donor tunneling involves inversion of the trimer. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Time-resolved spectroscopy that uses more than one incoherent excitation, and thus has multiple periods of time evolution, is becoming more common. A recent example is multiple population-period transient spectroscopy (MUPPETS), which is implemented as a high-order transient grating. In this paper, a formalism is developed to treat these types of incoherent spectroscopy in a manner that parallels the Liouville-pathway formalism used to treat multidimensional coherent spectroscopy. A Hilbert space of incoherent (population) states is defined and general expressions for transition and time-evolution operators acting on these states are derived from the corresponding quantum operators. This formalism describes incoherent experiments that involve an arbitrary number of temporal dimensions in terms of pathways through the Hilbert space. Each pathway is associated with a multiple-time rate-correlation function. Previous work has shown that these multiple-time correlation functions can measure heterogeneity in electronic-relaxation rates. Thus, they are an analog of coherent “echo” experiments, which measure heterogeneity in frequencies. We show that similar “MUPPETS echo” experiments can be done on any incoherent variable. For a dilute molecular solute, the Hilbert-space method leads to a systematic treatment of multidimensional transient gratings. The extension of irreducible-tensor methods to the incoherent Hilbert space results in a classification of orientational gratings of arbitrary order. The general methods developed in this paper are applied more specifically to single-photon, dipole transitions in the following paper. [ABSTRACT FROM AUTHOR]

For coherent Raman spectroscopies, common femtosecond pulses often lie in an intermediate regime: their bandwidth is too wide for measurements in the frequency domain, but their temporal width is too broad for homodyne measurements in the time domain. A recent paper [S. Nath et al., Phys. Rev. Lett. 97, 267401 (2006)] showed that complete Raman spectra can be recovered from intermediate length pulses by using simultaneous time and frequency detection (TFD). Heterodyne detection and a phase-stable local oscillator at the anti-Stokes frequency are not needed with TFD. This paper examines the theory of TFD Raman in more detail; a companion paper tests the results on experimental data. Model calculations illustrate how information on the Raman spectrum is transferred from the frequency domain to the time domain as the pulse width shortens. When data are collected in both dimensions, the Raman spectrum is completely determined to high resolution, regardless of the probe pulse width. The loss of resolution in many femtosecond coherent Raman experiments is due to the restriction to one-dimensional data collection, rather than due to a fundamental restriction based on the pulse width. [ABSTRACT FROM AUTHOR]

The preceding paper showed that, in principle, a high-resolution coherent Raman spectrum can be recovered using femtosecond probe pulses by combined detection in both time and frequency. This measurement is possible even when the pulses are too broad in frequency for conventional frequency-domain spectroscopy and too broad in time for conventional time-domain spectroscopy. In this paper, the method is tested on experimental coherent anti-stokes Raman spectroscopy data from acetonitrile. Compared to theoretical models, experimental data are complicated by noise and incomplete knowledge of the pulse structure. Despite these complications, most of the information in the Raman spectrum is recovered from the data: weak transitions are detected and natural-linewidth resolution is achieved across an 800 cm-1 spectral range. However, circumstances in which experimental limitations result in missed features or ambiguities in the recovered spectrum are also identified. These results suggest where improvements in measurement and data analysis can be made. [ABSTRACT FROM AUTHOR]

Fluorescence line narrowing spectroscopy is extended to the study of liquid state dynamics. Measurements are made on solutions of dimethyl-s-tetrazine in glycerol from room temperature to below the glass transition. The structural broadening identified in the preceding paper is related to a relaxation function by the use of a simple configuration coordinate model. This relaxation function is ∼150 times faster than the structural relaxation function measured by other experiments, showing that electronic state solvation is sensitive to a unique aspect of the structural dynamics of the liquid. [ABSTRACT FROM AUTHOR]

In this paper, the results of the modeling calculations carried out for predicting the interference effects expected in the sum frequency generation (SFG) spectra of a specific thin-layer system, described in the accompanying paper, are tested by comparing them with the experimental spectra obtained for a real thin-layer film comprising an organic monolayer/variable thickness dielectric layer/gold substrate. In this system, two contributions to the SFG spectra arise, a resonant contribution from the organic film and a nonresonant contribution from the gold substrate. The modeling calculations are in excellent agreement with the experimental spectra over a wide range of thicknesses and for different polarization combinations. The introduction of another resonant monolayer adjacent to the gold substrate and with the molecules having a reverse orientation has a significant affect on the spectral shapes which is predicted. If a dielectric substrate such as CaF2 is used instead of a gold substrate, only the spectral intensities vary with the film thickness but not the spectral shapes. The counterpropagating beam geometry will change both the thickness dependent spectral shapes and the intensity of different vibrational modes in comparison with a copropagating geometry. The influences of these experimental factors, i.e., the molecular orientational structure in the thin film, the nature of the substrate, and the selected incident beam geometry, on the experimental SFG spectra are quantitatively predicted by the calculations. The thickness effects on the signals from a SFG active monolayer contained in a thin liquid-layer cell of the type frequently used for in situ electrochemical measurements is also discussed. The modeling calculation is also valid for application to other thin-film systems comprising more than two resonant SFG active interfaces by appropriate choice of optical geometries and relevant optical properties. [ABSTRACT FROM AUTHOR]

The peak-sorting capabilities of high resolution coherent two-dimensional (2D) spectroscopy provide a new way of dealing with severe rotational congestion. This paper describes the application of this technique to the polyatomic molecule, NO2. NO2 is a primary component of photochemical smog and has a notoriously complex and congested spectrum that extends from the infrared to the ultraviolet regions. This spectrum is infamous for having an unusually high density of peaks and very few regular patterns. However, the coherent 2D spectrum of NO2 shows a network consisting of numerous X-shaped patterns that mark the locations of vibronic origins. This paper describes how peak sorting leads to the formation of such patterns and how peak coupling can be used to conduct a rotational analysis of congested areas in the visible spectrum of NO2. [ABSTRACT FROM AUTHOR]

Surfaces and interfaces play important roles in many processes and reactions and are therefore intensively studied, often with the aim of obtaining molecular-level information from just the interfacial layer. Generally, only the first few molecular layers next to the interface are relevant for the surface processes. In the past decades, 2nd-order nonlinear spectroscopies including sum-frequency generation and second harmonic generation have developed into powerful tools for obtaining molecularly specific insights into the interfacial region. These approaches have contributed substantially to our understanding of a wide range of physical phenomena. However, along with their wide-ranging applications, it has been realized that the implied surface-specificity of these approaches may not always be warranted. Specifically, the bulk quadrupole contribution beyond the electric dipole-approximation for a system with a weak nonlinear interface signal, as well as the diffuse layer contribution at charged interfaces, could mask the surface information. In this perspective paper, we discuss the surface-specificity of 2nd-order nonlinear spectroscopy, especially considering these two contributions. [ABSTRACT FROM AUTHOR]

The calculation of rovibrational transition energies and intensities is often hampered by the fact that vibrational states are strongly coupled by Coriolis terms. Because it invalidates the use of perturbation theory for the purpose of decoupling these states, the coupling makes it difficult to analyze spectra and to extract information from them. One either ignores the problem and hopes that the effect of the coupling is minimal or one is forced to diagonalize effective rovibrational matrices (rather than diagonalizing effective rotational matrices). In this paper we apply a procedure, based on a quantum mechanical canonical transformation for deriving decoupled effective rotational Hamiltonians. In previous papers we have used this technique to compute energy levels. In this paper we show that it can also be applied to determine intensities. The ideas are applied to the ethylene molecule. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper, we extend and elaborate upon a wavelet method first presented in a previous publication [B. Poirier, J. Theo. Comput. Chem. 2, 65 (2003)]. In particular, we focus on construction and optimization of the wavelet functions, from theoretical and numerical viewpoints, and also examine their localization properties. The wavelets used are modified Wilson-Daubechies wavelets, which in conjunction with a simple phase space truncation scheme, enable one to solve the multidimensional Schrödinger equation. This approach is ideally suited to rovibrational spectroscopy applications, but can be used in any context where differential equations are involved. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Femtosecond primary events in bacteriorhodopsin BR and its retinal modified analogs are discussed. Ultrafast time resolved electronic spectra of the primary intermediates induced in the BR photocycle are discussed along with spectral and kinetic inconsistencies of the previous models proposed in the literature. The theoretical model proposed in this paper based on vibrational coupling between the electronic transition of the chromophore and intramolecular vibrational modes allows us to calculate the equilibrium electronic absorption band shape and the hole burning profiles. The model is able to rationalize the complex pattern of behavior for the primary events in BR and explain the origin of the apparent inconsistencies between the experiment and the previous theoretical models. The model presented in the paper is based on the anharmonic coupling assumption in the adiabatic approximation using the canonical transformation method for diagonalization of the vibrational Hamiltonian instead of the commonly used perturbation theory. The electronic transition occurs between the Born—Oppenheimer potential energy surfaces with the electron involved in the transition being coupled to the intramolecular vibrational modes of the molecule (chromophore). The relaxation of the excited state occurs by indirect damping (dephasing) mechanisms. The indirect dephasing is governed by the time evolution of the anharmonic coupling constant driven by the resonance energy exchange between the intramolecular vibrational mode and the bath. The coupling with the intramolecular vibrational modes results in the Franck—Condon progression of bands that are broadened due to the vibrational dephasing mechanisms. The electronic absorption line shape has been calculated based on the linear response theory whereas the third order nonlinear response functions have been used to analyze the hole burning profiles obtained from the pump—probe time-resolved measurements. The theoretical treatment proposed in this paper provides a basis for a substantial revision of the commonly accepted interpretation of the primary events in the BR photocycle that exists in the literature. [ABSTRACT FROM AUTHOR]

Emissions in the 200–750 nm region produced by the collision of He[sup *](2 [sup 3]S) with H[sub 2]S were studied under single-collision conditions. The hydrogen Balmer lines and the SH[sup +](A [sup 3]Π–X [sup 3]Σ[sup -]) and H[sub 2]S[sup +](à [sup 2]A[sub 1]–X [sup 2]B[sub 1]) bands were assigned. The total emission cross section (σ[sub em]) was evaluated to be (1.7±0.3)×10[sup -20] m[sup 2] at a collision energy of 150 meV. The σ[sub em]s of the SH[sup +](A–X) and H[sub 2]S[sup +](ÖX) bands decreased with increase in the collision energy in the 115–200 meV range, indicating that attractive forces are effective for the incident channels with regard to the formation of these species. The rotational distribution of SH[sup +](A [sup 3]Π,ν[sup ′]=0) is represented by a Boltzmann temperature of 870±80 K. The H[sub 2]S[sup +](à [sup 2]A[sub 1]–X [sup 2]B[sub 1]) emission, which was assigned for the first time in the Penning ionization of H[sub 2]S, primarily consists of the bending progressions. The internal populations of H[sub 2]S[sup +](Ã) were analyzed using the vibrational energies and Einstein’s A coefficients calculated in this study. The details of the calculation and derived spectroscopic constants are reported in the accompanying paper, Paper I. The populations obtained for the bending vibration (ν[sub 2][sup ′]) of H[sub 2]S[sup +](Ã) show an inverted distribution with a peak at ν[sub 2][sup ′]=3. This distribution is shifted lower compared that with a peak at ν[sub 2][sup ′]=4–5 observed by He[sup *](2 [sup 3]S) Penning ionization electron spectroscopy and that with a peak at ν[sub 2][sup ′]=6–7 predicted by the theoretical Franck–Condon factors for the H[sub 2]S(X)–H[sub 2]S[sup +](Ã) ionization. The origin of the difference is discussed concerning the formation mechanism of H[sub 2]S[sup +](à [sup 2]A[sub 1]). © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present semiclassical calculations of the infrared line shapes for the three intramolecular vibrations of dilute HOD in liquid D[SUB2]O. In these calculations the vibrations of HOD are treated quantum mechanically, and the rotations and translations of all the molecules are treated classically. The approach and model, which is based on earlier work of Oxtoby and of Rey and Hynes, was discussed in detail in Paper I, on vibrational energy relaxation in the same system, of this series. A novel feature of our approach is a self-consistent renormalization scheme for determining the system and bath Hamiltonians for a given vibrational state of the HOD molecule. Our results for the line shapes are in reasonable agreement with experiment. We also explore the extent to which the frequency fluctuations leading to the line shape are Gaussian. Finally, we calculate the vibrational Stokes shift for the OH stretch fundamental. Our result, which is nonzero only because the specification of the bath Hamiltonian depends on the vibrational state of the HOD molecule (as a result of the self-consistent renormalization scheme), is 57 cm[SUP-1], in good agreement with the experimental number of 70 cm[SUP-1]. [ABSTRACT FROM AUTHOR]

The Robert-Bonamy formalism has been commonly used to calculate half-widths and shifts of spectral lines for decades. This formalism is based on several approximations. Among them, two have not been fully addressed: the isolated line approximation and the neglect of coupling between the translational and internal motions. Recently, we have shown that the isolated line approximation is not necessary in developing semi-classical line shape theories. Based on this progress, we have been able to develop a new formalism that enables not only to reduce uncertainties on calculated half-widths and shifts, but also to model line mixing effects on spectra starting from the knowledge of the intermolecular potential. In our previous studies, the new formalism had been applied to linear and asymmetric-top molecules. In the present study, the method has been extended to symmetric-top molecules with inversion symmetry. As expected, the inversion splitting induces a complete failure of the isolated line approximation. We have calculated the complex relaxation matrices of selfbroadened NH3. The half-widths and shifts in the ν1 and the pure rotational bands are reported in the present paper. When compared with measurements, the calculated half-widths match the experimental data very well, since the inapplicable isolated line approximation has been removed. With respect to the shifts, only qualitative results are obtained and discussed. Calculated off-diagonal elements of the relaxation matrix and a comparison with the observed line mixing effects are reported in the companion paper (Paper II). [ABSTRACT FROM AUTHOR]

Several commonly used approximate methods for the calculation of vibration–rotation–tunneling spectra for (HCl)2 are described. These range from one-dimensional models to an exact coupled four-dimensional treatment of the intermolecular dynamics. Two different potential surfaces were employed—an ab initio and our ES1 experimental surface (determined by imbedding the four-dimensional calculation outlined here in a least-squares loop to fit the experimental data, which is described in the accompanying paper [J. Chem. Phys. 103, 933 (1995)]. The most important conclusion deduced from this work is that the validity of the various approximate models is extremely system specific. All of the approximate methods addressed in this paper were found to be sensitive to the approximate separability of the radial and angular degrees of freedom, wherein exists the primary difference between the two potentials. Of particular importance, the commonly used reversed adiabatic angular approximation was found to be very sensitive to the choice for fixed R; an improper choice would lead to results very much different from the fully coupled results and perhaps to false conclusions concerning the intermolecular potential energy surface. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper we analyze the vibrational spectra of the Σ+g ground state of CS2, the experimental results of which have been described in a forth coming paper. We show that, up to 12 000 cm-1, CS2 can be described by a system of two degrees of freedom strongly coupled by a 1:2 type Fermi resonance. The corresponding vibrational spectra are refitted with the aid of only seven parameters. Analysis of the spectra by the statistical Fourier transform technique reveals stroboscopic effects between the symmetric stretching mode and the bending mode. The distinction between the ‘‘stroboscopic hole’’ due to these effects and the ‘‘correlation hole’’ due to nonintegrable terms in the Hamiltonian is discussed in detail. The study of the topology of the phase space of CS2 in the regular and chaotic cases is carried out in the basis described by a vibrational angular momentum which includes the Fermi resonance. We show the analogy between the localization of the wave packets of the eigenstates and the trajectories. We also show the destabilization of the trajectories due to a term in the Hamiltonian which couples neighboring polyads and which is a second Fermi resonance. We show that only two resonances are enough to induce a chaotic situation. [ABSTRACT FROM AUTHOR]

Destructive quantum interference in single molecule electronics is an intriguing phenomenon; however, distinguishing quantum interference effects from generically low transmission is not trivial. In this paper, we discuss how quantum interference effects in the transmission lead to either low current or a particular line shape in current-voltage curves, depending on the position of the interference feature. Second, we consider how inelastic electron tunneling spectroscopy can be used to probe the presence of an interference feature by identifying vibrational modes that are selectively suppressed when quantum interference effects dominate. That is, we expand the understanding of propensity rules in inelastic electron tunneling spectroscopy to molecules with destructive quantum interference. [ABSTRACT FROM AUTHOR]

We present an ab initio quantum study of the photoelectron spectra of sulfur dioxide, based on wavepacket propagations on manifolds of ionic, and excited/Rydberg states. We obtain excellent agreement for two different cases. First, the one photon ionization case where we can reproduce all details of the experimental spectrum and demonstrate the influence of the conical intersection between two of the ionic states. Then the multiphoton ionization regime, in which the dynamics of the wave packet on the two lowest singlet states is directly mapped in the spectra via a pump-probe scheme, as proposed in the experimental companion paper [I. Wilkinson et al., J. Chem. Phys. 140, 204301 (2014)]. [ABSTRACT FROM AUTHOR]

Semiclassical (SC) vibrational spectroscopy is a technique capable of reproducing quantum effects (such as zero-point energies, quantum resonances, and anharmonic overtones) from classical dynamics runs even in the case of very large dimensional systems. In a previous study [Conte et al. J. Chem. Phys. 151, 214107 (2019)], a preliminary sampling based on adiabatic switching has been shown to be able to improve the precision and accuracy of semiclassical results for challenging model potentials and small molecular systems. In this paper, we investigate the possibility to extend the technique to larger (bio)molecular systems whose dynamics must be integrated by means of ab initio "on-the-fly" calculations. After some preliminary tests on small molecules, we obtain the vibrational frequencies of glycine improving on pre-existing SC calculations. Finally, the new approach is applied to 17-atom proline, an amino acid characterized by a strong intramolecular hydrogen bond.

In this paper, we theoretically investigate the nuclear signatures effects, i.e., the initial vibrational state and the isotopic effects on the generations of the molecular high-order harmonics and the attosecond pulses when the model H2+/D2+ ions are exposed to a 5 fs/800 nm chirp pulse. The numerical solution of the time-dependent Schrödinger equation for these vibrating molecule ions shows that the intensities of the harmonic spectra are reinforced with the enhancement of the initial vibrational state. Moreover, through the investigation of the isotopic effect, we find that more intense harmonics are generated in the lighter nucleus. Furthermore, by optimizing the chirp pulse under the optimal initial vibrational state, an intense ultrabroad supercontinuum with a 325 eV bandwidth can be obtained. By properly superposing the harmonic spectrum, an attosecond pulse as short as 57 as (16 as) is generated without (with) phase compensation. [ABSTRACT FROM AUTHOR]

The jet-cooled high resolution spectrum of the vibrationless Ã←X transition of the deuterated species of the methyl peroxy radical has been recently published in this journal (S. Wu, P. Dupré, P. Rupper, and T. A. Miller, J. Chem. Phys. 127, 224305 (2007)). The spectrum was analyzed using a rigid-rotor model with quadratic spin-rotation coupling. The analysis was based on the fit of ∼350 partially resolved line positions and was quite satisfactory. However, the full simulation of the spectral intensity clearly identifies a lack of ability to reproduce relatively small line clumps ('extra' lines) located between the two main central Q branches. This is indicating of an incomplete initial analysis. In the present paper we reanalyze this electronic transition by considering a reference-frame axis-switching resulting from the nuclear rearrangement associated to the electronic transition (spectra obtained at two different temperatures are considered). The potential energy hypersurfaces of the two electronic states are sufficiently dissimilar to induce changes in the molecule geometry, particularly, the angle COO⁁, which induces a rotation (∼1.7°) of the principal axes of inertia located in the molecule symmetry plane. The present analysis is supported by a global fitting of the spectrum intensity and gives rise to a slightly different set of molecular constants. Attention is paid to the wavefunction symmetry assignment of a non-orthorhombic molecule. Couplings due to the torsion of the methyl group are discussed in the following paper (P. Dupre, J. Chem. Phys. 134, 244309 (2011)). [ABSTRACT FROM AUTHOR]

Disorder plays an important role in the photophysics of conjugated polymers such as poly(para-phenylene vinylene) (PPV). The dipole moments measured by electroabsorption spectroscopy for a centrosymmetric system such as PPV provide a direct quantitative measure of disorder-induced symmetry breaking. Although inner-sphere (structural) disorder is present, outer-sphere (environmental) disorder dominates the symmetry breaking in PPV. This paper develops and compares six models of outer-sphere disorder that differ in their representation of the electrostatic environment of PPV in glassy solvents. The most detailed model is an all-atom description of the solvent glass and this model forms the basis for comparison of the less detailed models. Four models are constructed in which multipoles are placed at points on a lattice. These lattice models differ in the degree to which they include correlation between the lattice spacings and the orientations of the multipoles. A simple model that assigns random Gaussian-distributed electrostatic potentials to each atom in the PPV molecule is also considered. Comparison of electronic structure calculations of PPV in these electrostatic environments using the all-atom model as a benchmark reveals that dipole and quadrupole lattices provide reasonable models of organic glassy solvents. Including orientational correlation among the solvent molecules decreases the effects of outer-sphere disorder, whereas including correlation in the lattice spacings increases the effects. Both the dipole and quadrupole moments of the solvent molecules can have significant effects on the symmetry breaking and these effects are additive. This additivity provides a convenient means for predicting the effects of various glassy solvents based on their multipole moments. The results presented here suggest that electrostatic disorder can account for the observed symmetry breaking in organic glasses. Furthermore, the lattice models are in general agreement with the dipole and quadrupole lattice models used to explain the Poole–Frenkel behavior in charge transport through disordered organic materials. [ABSTRACT FROM AUTHOR]

The formalism developed in the preceding paper for vibrational autoionization via Renner–Teller active vibrations is adapted to treat dissociative recombination and applied to the reaction of HCO++e-. Existing spectroscopic data on the rovibrational structure of the HCO+ 2Σ+ ion and the HCO 3pπ 2Π Rydberg state are fitted by using the semirigid bender model to extract the parameters required to calculate the autoionization and electron capture widths. The results of this simple model are in good agreement with more detailed first principles calculations of the dissociative recombination cross section and confirm the earlier conclusion that coupling due to the Renner–Teller interaction is largely responsible for the observed dissociative recombination cross section at electron energies below ∼0.1 eV. [ABSTRACT FROM AUTHOR]

Optical response functions are known to reflect quantum dynamics in a superposition state and as such, lack a well-defined classical limit. In a previous paper we considered the importance of accounting for the quantum nature of the dynamics by comparing the linear absorption spectrum and homodyne-detected time-integrated two-pulse photon-echo signal as calculated via the semiclassical forward-backward approach, linearized semiclassical approach, and standard approach which is based on equilibrium ground state dynamics [Shi and Geva, J. Chem. Phys. 122, 064506 (2005)]. In the present paper, we extend the comparison to the case of heterodyne-detected and time-resolved nonlinear time-domain rephasing and nonrephasing signals generated in three-pulse experiments and the corresponding frequency-domain two-dimensional spectra. The comparison is performed in the context of a two-state chromophore solvated in a nonpolar liquid. It is shown that the inherent insensitivity of the standard method to the nonequilibrium dynamics on the excited state potential surface gives rise to two-dimensional spectra which are symmetrical relative to the diagonal. In contrast, accounting for the effect of nonequilibrium excited state dynamics, as is the case within the forward-backward and linearized semiclassical methods, is found to give rise to two-dimensional spectra that become increasingly asymmetrical relative to the diagonal as the waiting time between the second and third pulses becomes larger. It is argued that the emergence of the asymmetry provides a useful probe of nonequilibrium solvation on the excited state potential surface. [ABSTRACT FROM AUTHOR]

In the present paper, the ion dynamics and relaxation of fluoride ions in Pb1-xSnxF2 (with x=0.2–0.6) solid solutions, prepared by mechanochemical milling, are studied in the conductivity formalism over wide ranges of frequencies and temperatures. The conductivity spectra of the investigated materials are analyzed by the Almond-West (AW) power-law model. The estimated values of the hopping rates and the dc conductivity of different compositions are thermally activated with almost the same activation energy. The calculated values of the concentration of mobile ions, nc, are almost independent of temperature and composition for x=0.2–0.4. The maximum value of nc is obtained for the x=0.6 sample, although it does not show the maximum conductivity. Therefore, the composition dependence of the ionic conductivity of these solid solutions could be explained based on the extracted parameters. The results presented in the current work indicate that the AW model represents a reasonable approximation of the overall frequency-dependent conductivity behavior of the investigated materials. The conductivity spectra at different temperatures for each composition are successfully scaled to a single master curve, indicating a temperature-independent relaxation mechanism. For different compositions, however, the conductivity spectra cannot be scaled properly, indicating composition-dependent relaxation dynamics. [ABSTRACT FROM AUTHOR]

In this paper, we introduce algorithms based on Fourier synthesis for designing phase compensating rf pulse sequences for high-resolution nuclear magnetic resonance (NMR) spectroscopy in an inhomogeneous B0 field. We show that using radio frequency pulses and time varying linear gradients in three dimensions, it is possible to impart the transverse magnetization of spins phase, which is a desired function of the spatial (x,y,z) location. Such a sequence can be used to precompensate the phase that will be acquired by spins at different spatial locations due to inhomogeneous magnetic fields. With this precompensation, the chemical shift information of the spins can be reliably extracted and high resolution NMR spectrum can be obtained. [ABSTRACT FROM AUTHOR]

Spectral methods based on nonclassical polynomials and Fourier basis functions or sinc interpolation techniques are compared for several eigenvalue problems for the Fokker-Planck and Schrödinger equations. A very rapid spectral convergence of the eigenvalues versus the number of quadrature points is obtained with the quadrature discretization method (QDM) and the appropriate choice of the weight function. The QDM is a pseudospectral method and the rate of convergence is compared with the sinc method reported by Wei [J. Chem. Phys., 110, 8930 (1999)]. In general, sinc methods based on Fourier basis functions with a uniform grid provide a much slower convergence. The paper considers Fokker-Planck equations (and analogous Schrödinger equations) for the thermalization of electrons in atomic moderators and for a quartic potential employed to model chemical reactions. The solution of the Schrödinger equation for the vibrational states of I2 with a Morse potential is also considered. [ABSTRACT FROM AUTHOR]

In this paper we report two improvements on the approach we have used to compute rovibrational levels of methane and apply the new ideas to calculate rovibrational levels of two methane isotopomers CH3D and CHD3. Both improvements make the bend calculation better. The first improvement is a G6-invariant (or C3υ-invariant) grid which is designed such that each point on the grid is mapped to another point on the grid by any of the G6 operations. The second improvement is the use of fast Fourier transform (FFT) to compute the bend potential matrix-vector products. The FFT matrix-vector product is about three and ten times faster than the previous sequential summation method for the J=0 and J>0 cases, respectively. The calculated J=1 rovibrational levels of CH3D and CHD3 on the Schwenke and Partridge [Spectrochim. Acta, Part A 57, 887 (2001)] ab initio potential are in good agreement (within 6 cm-1 for the levels up to 3000 cm-1) with the experimental data. The agreement is even better (within 0.1 cm-1 for the levels up to 6000 cm-1) if the associated J=0 energies are subtracted. [ABSTRACT FROM AUTHOR]

High-level ab initio potential-energy curves and transition dipole moments for the OH X 2Π, 2 2Π, 1 2Σ-, D 2Σ-, 3 2Σ-, A 2Σ+, B 2Σ+, 1 2Δ, 1 4Σ-, and 1 4Π states are computed. The results are used to estimate the (2+1) resonance enhanced multiphoton ionization spectrum for the (D,3)2Σ-(υ′)←2hνX 2Π(υ″) transitions, which are compared with experiments by Greenslade et al. [see M. E. Greenslade, M. I. Lester, D. C. Radenovic, J. A. van Roij, and D. H. Parker, J. Chem. Phys. 123, 074309 (2005), preceeding paper]. We use the discrete variable representation-absorbing boundary condition method to incorporate the effect of the dissociative intermediate 1 2Σ- state. We obtain qualitative agreement with experiment for the line strengths. Radiative and predissociative decay rates of the Rydberg (D,3)2Σ- states of OH and OD were computed, including spin-orbit coupling effects and the effect of spin-electronic and gyroscopic coupling. We show that the lifetime of the Rydberg 2Σ- states for rotationally cold molecules is limited mainly by predissociation caused by spin-orbit coupling. [ABSTRACT FROM AUTHOR]

The interaction of formic acid (HCOOH) with solid water, deposited on tungsten at 80 K, was investigated. We have prepared and annealed formic acid (FA)/water interfaces (FA layers on thin films of solid water and H2O adlayers on thin FA films). Metastable impact electron spectroscopy and ultraviolet photoemission spectroscopy (He I and II) were utilized to study the electron emission from the 10a′ to 6a′ molecular orbitals (MOs) of FA, and the 1b1, 3a1, and 1b2 MOs of H2O. These spectra were compared with results of density-functional theory calculations on FA-H2O complexes reported in Ref. 14 [A. Allouche, J. Chem. Phys. 122, 234703(2005), (preceding paper)]. Temperature programmed desorption was applied for information on the desorption kinetics. Initially, FA is adsorbed on top of the water film. The FA spectra are distorted with respect to those from FA monomers; it is concluded that a strong interaction exists between the adsorbates. Even though partial solvation of FA species takes place during annealing, FA remains in the top layer up to the desorption of the water film. When H2O molecules are offered to FA films at 80 K, no water network is formed during the initial stage of water exposure; H2O molecules interact individually via H bonds with the formic acid network. Experiment and theory agree that no water-induced deprotonation of the formic acid molecules takes place. [ABSTRACT FROM AUTHOR]

The methods of stimulated emission pumping-hole-filling spectroscopy (SEP-HFS) and population transfer spectroscopy (SEP-PTS) were used to place direct experimental bounds on the energetic barriers to conformational isomerization in 3-indole-propionic acid (IPA) and its water-containing complex. By contrast with tryptamine (Paper I), IPA has only two conformations with significant population in them. The structures of the two conformers are known from previous work [P. M. Felker, J. Phys. Chem. 96, 7844 (1992)]. The energy thresholds for A→B and B→A isomerizations are placed at 854 and 754 cm-1, respectively. Lower bounds on the isomerization barrier in the two directions are determined from the last transition not observed in the SEP-PT spectra. These are placed at 800 and 644 cm-1 for A→B and B→A, respectively. The combined results place bounds on the relative energies of the A and B minima, with E(B)-E(A)=46–210 cm-1. Like the IPA monomer, the IPA-H2O complex forms two conformational isomers. Both these isomers incorporate the water molecule as a bridge between the carbonyl and OH groups of the carboxylic acid. Previous rotational coherence measurements (L. L. Connell, Ph.D. thesis, UCLA, 1991) have determined that these complexes retain the same IPA conformational structure as the monomers. SEP-PTS and SEP-HFS were carried out on the IPA-H2O complexes. It was demonstrated that it is possible to use SEP to drive conformational isomerization between the two conformational isomers of IPA-H2O. Bounds on the energy barriers to conformational isomerization are not effected greatly by the presence of the water molecule, with Ebarrier(A→B)=771–830 cm-1 and Ebarrier(B→A)=583–750 cm-1. This is a simple consequence of the fact that the barrier is an intramolecular barrier, and the water molecule is held fixed in the COOH pocket, where it interacts with the ring only peripherally during the isomerization process. Finally, changes in the SEP-PT spectral intensity in transitions near the top of the barrier to isomerization as a function of the position of SEP excitation relative to the pulsed valve exit provide some insight to the competition between vibrational relaxation and isomerization in a molecule the size of IPA. [ABSTRACT FROM AUTHOR]

Fragment analyses of vibrational circular dichroic response of dipeptides were carried out recently [Choi and Cho, J. Chem. Phys. 120, 4383 (2004)]. In the present paper, by using a minimal size unit peptide containing two chiral carbons covalently bonded to the peptide group, a generalized fragmentation approximation method is discussed and applied to the calculations of infrared-absorption and vibrational circular dichroism (VCD) intensities of amide I vibrations in various secondary structure polypeptides. Unlike the dipole strength determining IR-absorption intensity, the rotational strength is largely determined by the cross terms that are given by the inner product between the transition electric dipole and the transition magnetic dipole of two different peptides. This explains why the signs and magnitudes of VCD peaks are far more sensitive to the relative orientation and distance between different peptide bonds in a given protein. In order to test the validity of fragmentation approximation, three different segments in a globular protein ubiquitin, i.e., right-handed α-helix, β-sheet, and β-turn regions, were chosen for density-functional theory (DFT) calculations of amide I vibrational properties and the numerically simulated IR-absorption and VCD spectra by using the fragmentation method are directly compared with DFT results. It is believed that the fragmentation approximation method will be of use in numerically simulating vibrational spectra of proteins in solutions. [ABSTRACT FROM AUTHOR]

Time-resolved terahertz spectroscopy has become a widely used experimental tool for the investigation of ultrafast dynamics of polar systems in the far infrared. We have recently proposed an analytical method for the extraction of a transient two-dimensional susceptibility from the experimental data [Neˇmec, Kadlec, and Kuzˇel, J. Chem. Phys. 117, 8454 (2002)]. In the present paper the methodology of optical pump-terahertz probe experiments is further developed for direct application in realistic experimental situations. The expected two-dimensional transient response function is calculated for a number of model cases (including Drude dynamics of free carriers, harmonic and anharmonic oscillator modes); these results serve as a basis for the interpretation of experimental results. We discuss also the cases where only partial (one-dimensional) information about the system dynamics can be experimentally obtained. [ABSTRACT FROM AUTHOR]

Hybrid molecular dynamics (MD) simulations, which combine density functional theory (DFT) descriptions of a molecule with a molecular mechanics (MM) modeling of its solvent environment, have opened the way towards accurate computations of solvation effects in the vibrational spectra of molecules. Recently, Wheeler et al. [ChemPhysChem 4, 382 (2002)] have suggested to compute these spectra from DFT/MM-MD trajectories by diagonalizing the covariance matrix of atomic fluctuations. This so-called principal mode analysis (PMA) allegedly can replace the well-established approaches, which are based on Fourier transform methods or on conventional normal mode analyses. By scrutinizing and revising the PMA approach we identify five conditions, which must be guaranteed if PMA is supposed to render exact vibrational frequencies. Besides specific choices of (a) coordinates and (b) coordinate systems, these conditions cover (c) a harmonic intramolecular potential, (d) a complete thermal equilibrium within the molecule, and (e) a molecular Hamiltonian independent of time. However, the PMA conditions [(c)–(d)] and [(c)–(e)] are generally violated in gas phase DFT-MD and liquid phase DFT/MM-MD trajectories, respectively. Based on a series of simple analytical model calculations and on the analysis of MD trajectories calculated for the formaldehyde molecule in the gas phase (DFT) and in liquid water (DFT/MM) we show that in both phases the violation of condition (d) can cause huge errors in PMA frequency computations, whereas the inevitable violations of conditions (c) and (e), the latter being generic to the liquid phase, imply systematic and sizable underestimates of the vibrational frequencies by PMA. We demonstrate that the huge errors, which are caused by an incomplete thermal equilibrium violating (d), can be avoided if one introduces mode-specific temperatures Tj and calculates the frequencies from a “generalized virial” (GV) expression instead from PMA. Concerning ways to additionally remove the remaining errors, which GV still shares with PMA, we refer to Paper II of this work [M. Schmitz and P. Tavan, J. Chem. Phys. 121, 12247 (2004)]. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The profound differences between solids and liquids notwithstanding, high-frequency vibrational energy relaxation in liquids seems to be well described by assuming that the excess energy is being transferred into discrete overtones of some fundamental intermolecular vibrations—precisely the way it is in crystalline solids. In a solid-state context, this kind of analysis can be used to justify the observation that relaxation rates fall off exponentially with the energy being transferred. Liquids, however, have a substantial degree of disorder, causing their relevant intermolecular spectra to have correspondingly diffuse band edges and large bandwidths. It is therefore not at all obvious what should become of this exponential-gap-law phenomenology. We show in this paper how near exponential-gap-law behavior can still be derived for vibrational energy relaxation in liquids. To do so, we take advantage of the simple dynamics that the high-frequency relaxation has when it is launched from an individual instantaneous configuration. Interestingly, the physically relevant region turns out not to be true asymptotic limit of our formalism, but for realistic liquid parameters the behavior in the physical regime differs only slightly from an exact exponential-gap law and is strikingly independent of the details of the intermolecular spectra. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A procedure for the Raman spectra calculation of vitreous and molten silicates was presented in this paper. It includes molecular dynamics MD simulation for the generation of equilibrium configurations, Wilson’s GF matrix method for the calculations of eigenfrequencies and corresponding vectors, electro-optical parameters method (EOPM) for the Raman intensity calculations, and the bond polarizability model (BPM) for the determination of polarizability and polarizability derivative. One of the most important characteristics of this procedure is the achievement of the partial Raman spectra of five tetrahedral units, as well as the total spectral envelope. In this paper, the calculation was carried out for the vitreous and molten calcium silicates with different compositions and at various temperatures. It is worthwhile to note that the calculation is based on statistical configurations distribution in the space and so it is not needed to artificially adjust the full width at half maximum (FWHM) of spectra. It was also tested through the good agreement of the calculated spectra with the experimental, including some regularity of spectral properties. According to the calculation, the symmetrical stretching of whole tetrahedral units, to which the stretching of Si-Onb bond gives the main contribution to intensity, is proven to be the dominance in the high-frequency range (800–1200 cm-1) and the symmetrical bending of Si-Ob-Si, to which the stretching of Si-Ob bond exhibits the main contribution, is the dominance in the medium-frequency range (400–700 cm-1). As the first theoretical results, the Raman scattering coefficient of each Qi was found little change along with the variation of composition and temperature. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using the multiexciton density matrix theory of excitation energy transfer in chromophore complexes developed in a foregoing paper [J. Chem. Phys. 118, 746 (2003)], the computation of ultrafast transient absorption spectra is presented. Beside static disorder and standard mechanisms of excitation energy dissipation the theory incorporates exciton exciton annihilation (EEA) processes. To elucidate signatures of EEA in intensity dependent transient absorption data the approach is applied to the B850 ring of the LH2 found in rhodobacter sphaeroides. As main indications for two-exciton population and resulting EEA we found (i) a weakening of the dominant single-exciton bleaching structure in the transient absorption, and (ii) an intermediate suppression of long-wavelength and short-wavelength shoulders around the bleaching structure. The suppression is caused by stimulated emission from the two-exciton to the one-exciton state and the return of the shoulders follows from a depletion of two-exciton population according to EEA. The EEA-signature survives as a short-wavelength shoulder in the transient absorption if orientational and energetic disorder are taken into account. Therefore, the observation of the EEA-signatures should be possible when doing frequency resolved transient absorption experiments with a sufficiently strongly varying pump-pulse intensity. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The bound rovibronic levels of the He–HF[sup +] complex were calculated for total angular momentum J=1/2, 3/2, 5/2, 7/2, and 9/2 with the use of ab initio diabatic intermolecular potentials presented in Paper I and the inclusion of spin–orbit coupling. The character of the rovibronic states was interpreted by a series of calculations with the intermolecular distance R fixed at values ranging from 1.5 to 8.5 Å and by analysis of the wave functions. In this analysis we used approximate angular momentum quantum numbers defined with respect to a dimer body-fixed (BF) frame with its z axis parallel to the intermolecular vector R and with respect to a molecule-fixed (MF) frame with its z axis parallel to the HF[sup +] bond. The linear equilibrium geometry makes the He–HF[sup +] complex a Renner–Teller system. We found both sets of quantum numbers, BF and MF, useful to understand the characteristics of the Renner–Teller effect in this system. In addition to the properties of a “normal” semirigid molecule Renner–Teller system it shows typical features caused by large-amplitude internal (bending) motion. We also present spectroscopic data: stretch and bend frequencies, spin–orbit splittings, parity splittings, and rotational constants. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper, using density functional theory, we show the effects of explicit intermolecular hydrogen bonds on infrared spectra of glucose–water complexes. The number of explicit water molecules ranges from four to nine, and we approximate the rest of other water molecules as a continuum medium. When eight or nine water molecules are considered explicitly, our computed spectra are in good agreement with the main features of the experimental one. However, in the cases of explicit water molecules less than eight, our computed spectra are not improved successfully. This suggests that in predicting infrared spectrum of glucose in water the effects of explicit water molecules around the glucose molecule are not negligible. We also discuss the numbers of intermolecular hydrogen bonds, spectral differences between α and β anomers, and the main features of normal modes in the 1000–1200 cm-1 region. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In a previous theoretical study [J. Chem. Phys. 117, 5827 (2002)] we calculated the vibrational lifetimes of the three fundamentals of HOD in liquid D[SUB2]O. In that calculation the D[SUB2]O solvent was treated as rigid, not allowing for the possibility of intermolecular vibrational energy transfer as a relaxation mechanism. In this paper we use both flexible and rigid solvent models, enabling us to include the possibility of intermolecular vibrational energy transfer, and also to estimate branching ratios for vibrational and nonvibrational relaxation channels. Our theoretical value for the lifetime of the OH stretch decreases modestly from 2.7 ps (in the original calculation) to 2.3 ps, which should be compared to the experimental value of about 1 ps. The lifetime of the OD stretch decreases dramatically from 18 ps to 390 fs due to resonant energy transfer to the solvent stretch. Our lifetime value for the bend actually increases from 220 to 380 fs, not because of the vibrational energy transfer channel, but rather because we find that Fermi's Golden Rule (used in the original calculation) breaks down for this very fast process. We have calculated all the state-to-state rate constants for the low-lying vibrational energy levels of HOD, which allows us to construct and solve the vibrational master equation. We find that after excitation of the OH stretch, population flows into the HOD bend states (and to a lesser extent the OD stretch of HOD) on the time scale of 1 ps, in agreement with recent infrared pump/Raman probe measurements of Dlott and co-workers. From our results we estimate that for each quantum of OH stretch excitation, 0.26 quanta of solvent stretch is excited by direct intermolecular energy transfer, and yet we find, surprisingly, that there is almost no direct excitation of solvent bend. On the other hand, we suggest that because of the intramolecular Fermi resonance in D[SUB2]O, rapid intramolecular vibrational relaxation occurs from solvent... [ABSTRACT FROM AUTHOR]

Incorporation of fluorescent proteins into biochemical systems has revolutionized the field of bioimaging. In a bottom-up approach, understanding the photophysics of fluorescent proteins requires detailed investigations of the light-absorbing chromophore, which can be achieved by studying the chromophore in isolation. This paper reports a photodissociation action spectroscopy study on the deprotonated anion of the red Kaede fluorescent protein chromophore, demonstrating that at least three isomers-assigned to deprotomers-are generated in the gas phase. Deprotomer-selected action spectra are recorded over the S 1 ← S 0 band using an instrument with differential mobility spectrometry coupled with photodissociation spectroscopy. The spectrum for the principal phenoxide deprotomer spans the 480-660 nm range with a maximum response at ≈610 nm. The imidazolate deprotomer has a blue-shifted action spectrum with a maximum response at ≈545 nm. The action spectra are consistent with excited state coupled-cluster calculations of excitation wavelengths for the deprotomers. A third gas-phase species with a distinct action spectrum is tentatively assigned to an imidazole tautomer of the principal phenoxide deprotomer. This study highlights the need for isomer-selective methods when studying the photophysics of biochromophores possessing several deprotonation sites.

Liquid water's rich sub-picosecond vibrational dynamics arise from the interplay of different highand low-frequency modes evolving in a strong yet fluctuating hydrogen bond network. Recent studies of the OH stretching excitations of H2O indicate that they are delocalized over several molecules, raising questions about whether the bending vibrations are similarly delocalized. In this paper, we take advantage of an improved 50 fs time-resolution and broadband infrared (IR) spectroscopy to interrogate the 2D IR lineshape and spectral dynamics of the HOH bending vibration of liquid H2O. Indications of strong bend-stretch coupling are observed in early time 2D IR spectra through a broad excited state absorption that extends from 1500 cm-1 to beyond 1900 cm-1, which corresponds to transitions from the bend to the bend overtone and OH stretching band between 3150 and 3550 cm-1. Pump-probe measurements reveal a fast 180 fs vibrational relaxation time, which results in a hot-ground state spectrum that is the same as observed for water IR excitation at any other frequency. The fastest dynamical time scale is 80 fs for the polarization anisotropy decay, providing evidence for the delocalized or excitonic character of the bend. Normal mode analysis conducted on water clusters extracted from molecular dynamics simulations corroborate significant stretch-bend mixing and indicate delocalization of δHOH on 2-7 water molecules. [ABSTRACT FROM AUTHOR]

It has been extensively demonstrated through first principles quantum mechanics calculations that water exhibits strong hydrogen bond cooperativity. Equations of state developed from statistical mechanics typically assume pairwise additivity, meaning they cannot account for these 3-body and higher cooperative effects. In this paper, we extend a second order thermodynamic perturbation theory to correct for hydrogen bond cooperativity in 4 site water. We demonstrate that the theory predicts hydrogen bonding structure consistent spectroscopy, neutron diffraction, and molecular simulation data. Finally, we implement the approach into a general equation of state for water. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the relaxation dynamics of Sierpinski hexagon fractal polymer. The relaxation dynamics of this fractal polymer is investigated in the framework of the generalized Gaussian structure model using both Rouse and Zimm approaches. In the Rouse-type approach, by performing real-space renormalization transformations, we determine analytically the complete eigenvalue spectrum of the connectivity matrix. Based on the eigenvalues obtained through iterative algebraic relations we calculate the averaged monomer displacement and the mechanical relaxation moduli (storage modulus and loss modulus). The evaluation of the dynamical properties in the Rousetype approach reveals that they obey scaling in the intermediate time/frequency domain. In the Zimm-type approach, which includes the hydrodynamic interactions, the relaxation quantities do not show scaling. The theoretical findings with respect to scaling in the intermediate domain of the relaxation quantities are well supported by experimental results. [ABSTRACT FROM AUTHOR]

A Hamiltonian is derived for the rotating water trimer with three internal motions—the rotations of the monomers about their hydrogen bonds. We obtain an expression of the kinetic energy operator, which is a non-trivial extension of earlier heuristic forms used for the non-rotating trimer. The Coriolis coupling operator between the single-axis monomer angular momenta and the overall trimer rotation is given for the first time. To analyze the effects of the tunneling and Coriolis splittings on the energy levels of the trimer, we introduced a qualitative model for the pseudo-rotation and donor tunneling. By perturbation theory and application of the permutation-inversion groups G6 and G48 we obtain algebraic expressions for the splittings due to pseudo-rotation and donor tunneling, respectively. The pseudo-rotation does not produce any internal angular momentum and does not yield first order Coriolis splitting, but in second order the Coriolis coupling lifts various degeneracies and gives rise to observable J-dependent splittings. Donor tunneling splits every pseudo-rotation level into a quartet and those levels in this quartet that belong to the three-dimensional irreps of G48 into doublets. For J>=0 a rather complex pattern of larger (for the internal states with G6 labels k=±1 and ±2) and smaller (for the levels with k=0 and k=3) splittings is obtained, especially for the substates with |K|=1 which are Coriolis coupled to the K=0 substates. The results of calculations in the companion paper, together with the model introduced in the present paper, will be used to interpret all the tunneling splittings observed in high-resolution spectra of (H2O)3 and (D2O)3. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]