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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]

It is only relatively recently that it has become possible to use spectroscopy to track the solvation of a molecule as one proceeds from small solute-plus-solvent clusters, through bulk liquids, and into cryogenic matrices. One of the more surprising findings of such studies is that, in a number of noteworthy instances—such as with benzene dissolved in Ar—the solvent shifts of spectral lines in even apparently sizable clusters seem not to go smoothly into the bulk results. In this and the following paper we consider just what level of theoretical treatment is necessary in order to be able to account for the solvent shift of electronic spectra consistently in environments ranging from clusters to the bulk. As we discuss in some detail, neither continuum dielectric approaches nor sums of pair potentials can adequately describe the solvation. What we propose here, instead, is that the effects of nonpolar solvents can be treated fully microscopically by a model incorporating both local repulsive effects and longer-ranged dielectric effects. The latter contribution, resulting from the solvent’s polarizability, is formulated in terms of the so-called polarization modes of the solvent, which change with the detailed arrangement of the solute’s environment. We illustrate the ideas by showing that one can understand the optical spectroscopy of benzene in liquid Ar more or less quantitatively by using this model, and we point out some connections with analogous time-dependent solvation studies. The application of this same approach to clusters is described in the succeeding paper. [ABSTRACT FROM AUTHOR]

The analytical infinite order sudden (IOS) quantum theory of triatomic photodissociation, developed in paper I, is applied to study the indirect photodissociation of NOCl through a real or virtual intermediate state. The theory uses the IOS approximation for the dynamics in the final dissociative channels and an Airy function approximation for the continuum functions. The transition is taken as polarized in the plane of the molecule; symmetric top wave functions are used for both the initial and intermediate bound states; and simple semiempirical model potentials are employed for each state. The theory provides analytical expressions for the photofragment yield spectrum for producing particular final fragment ro-vibrational states as a function of the photon excitation energy. Computations are made of the photofragment excitation spectrum of NOCl in the region of the T1(13A″) ←S0(11A′) transition for producing the NO fragment in the vibrational states nNO=0, 1, and 2. The computed spectra for the unexcited nNO==0 and excited nNO=2 states are in reasonable agreement with experiment. However, some discrepancies are observed for the singly excited nNO=1 vibrational state, indicating deficiencies in the semiempirical potential energy surface. Computations for two different orientations of the in-plane transition dipole moment produce very similar excitation spectra. Calculations of fragment rotational distributions are performed for high values of the total angular momentum J, a feature that would be very difficult to perform with close-coupled methods. Computations are also made of the thermally averaged rotational energy distributions to simulate the conditions in actual supersonic jet experiments. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Intramolecular vibrational energy relaxation (IVR) in nitrous acid (HONO) is studied with the help of ultrafast two-color pump-probe spectroscopy. In a previous paper [V. Botan et al., J. Chem. Phys. 124, 234511 (2006)], it has been observed that trans-HONO cools through a cascade of overtones of one specific mode after pumping the OH stretch vibration. We had suggested that this cooling mode is the ONO bend vibration. Furthermore, molecules that have initially been excited by the OH stretch vibration of cis-HONO and then underwent isomerization follow the same relaxation pathway. In the present study, we extend the investigation of IVR of cis- and trans-HONO to the N=O stretch and HON bend spectral regions, finding further evidence that the bottleneck of trans cooling is indeed the ONO bend vibration. In combination with information on the anharmonic coupling constants of different modes, the energy relaxation dynamics preceding this cooling cascade can also be followed in unprecedented detail. [ABSTRACT FROM AUTHOR]

In recent years, sum-frequency generation (SFG) has been used to investigate numerous interfaces including aqueous interfaces. A longstanding challenge to interpretation of the SFG results, along with the related aqueous-solution infrared and Raman spectra, is a lack of connection between features in the broad hydrogen-bonded region and molecular-level interactions or configurations. This paper reports results of a newly developed polarization analysis of the generated sum-frequency signal as a function of wavelength both to deconvolute spectral resonances and to characterize the dynamic polarization associated with the resonances. Operationally, the polarization angle of the generated sum frequency is determined by identifying the null angle. The technique is hence termed polarization-angle null analysis or PAN. PAN applied to ice is very powerful; it reveals that the hydrogen-bonded region of the basal face of ice Ih contains at least five oscillators, each with a distinct polarization. The dynamic polarizability of the longest wavelength oscillator is nearly entirely transverse (perpendicular to the surface normal, i.e., in the surface plane); in contrast, the shortest wavelength oscillator is almost entirely longitudinal (along the surface normal). [ABSTRACT FROM AUTHOR]

The analysis by infrared spectroscopy of aqueous mixtures of NaI and CsCl was made in order to obtain information at the molecular level of the mixing of these two salts taken as model systems of strong electrolytes in water. In previous papers [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 2664 (2001) and J.-J. Max et al., ibid. 126, 184507 (2007)] it was reported that a pure salt in water forms pairs of monoions to which are attached a fixed number of water molecules, giving solvated water species. Due to their interaction with the ion pairs, the solvated water molecules are strongly perturbed, modifying the IR water spectrum being monitored. After taking the IR spectrum of pure water, a small volume of NaI 2M was added and the IR spectrum taken. Then a small volume of CsCl 2M was added and a new IR spectrum taken. This procedure was repeated to obtain a series of 38 spectra in the 0.05M–0.83M concentration range. Factor analysis made on the series revealed the presence of three types of water: pure water and two salt solvated waters. The number of solvated water molecules on the two salts taken together is ten. Since NaI and CsCl have, respectively, 3.5 and 3.0 solvated water molecules, it was concluded that a reaction occurred in the solutions forming NaCl and CsI that have, respectively, five water molecules each for a total of ten. The analysis of the spectra of the orthogonal factors supports this attribution. These results provide additional proof of ion pairing in water. Furthermore, comparing the band displacements and intensity variations observed on the solvated water species to that of pure water indicates that the dielectric milieu surrounding the ion pairs is not constant. These results do not support the classical view of Debye-Hückel that considers that the ions are independent and the dielectric milieu constant. The present results give some in situ information on the reaction that goes on in “simple” electrolyte systems whose reactivity and molecular organization are still not completely mastered. [ABSTRACT FROM AUTHOR]

In this paper, it is demonstrated that a Lorentzian line shape is predicted for a resonance interacting with a bath of equally spaced levels, even in the sparse, low density of states limit, if one performs an inhomogeneous average over the position of the bath states relative to the bright state. The implication for the spectroscopy of molecules in helium nanodroplets and possibly other samples with a significant size distribution is that coupling of excitations to phonons can lead to Lorentzian shaped transitions entirely from inhomogeneous broadening with no population relaxation in the sample. [ABSTRACT FROM AUTHOR]

We present data obtained by time-resolved terahertz spectroscopy in selected semiconducting and molecular systems exhibiting subpicosecond far-infrared dynamics. We use a frequency-domain method which eliminates the influence of instrumental functions and artifacts due to frequency mixing and yields a two-dimensional transient conductivity of the photoexcited sample. This technique enables improving the attainable experimental time resolution and allows a simple qualitative interpretation of the results without a priori modeling. The quantitative interpretation is based on the time-dependent Drude and damped harmonic oscillator models. [ABSTRACT FROM AUTHOR]

The midinfrared (MIR) spectra of molecules in polar solvents exhibit inhomogeneously broadened bands whose spectral positions are shifted as compared to the gas phase. The shifts are caused by interactions with structured solvation shells and the broadenings by fluctuations of these interactions. The MIR spectra can be calculated from hybrid molecular dynamics (MD) simulations, which treat the solute molecule by density functional theory and the solvent by molecular mechanics by the so-called instantaneous normal mode analysis (INMA) or by Fourier transforming the time correlation function (FTTCF) of the molecular dipole moment. In Paper I of this work [M. Schmitz and P. Tavan, J. Chem. Phys. 121, 12233 (2004)] we explored an alternative method based on generalized virial (GV) frequencies noting, however, that GV systematically underestimates frequencies. As shown by us these artifacts are caused by solvent-induced fluctuations of the (i) equilibrium geometry, (ii) force constants, and (iii) normal mode directions as well as by (iv) diagonal and (v) off-diagonal anharmonicities. Here we now show, by analyzing the time scales of fluctuations and sample MD trajectories of formaldehyde in the gas phase and in water, that all these sources of computational artifacts can be made visible by a Fourier analysis of the normal coordinates. Correspondingly, the error sources (i) and (iii)–(v) can be removed by bandpass filtering, as long as the spectral signatures of the respective effects are well separated from the fundamental band. Furthermore, the artifacts arising from effect (ii) can be strongly diminished by a time-resolved version of the GV approach (TF-GV). The TF-GV method then yields for each mode j a trajectory of the vibrational frequency ωj(t|τ) at a time resolution τ>τj, which is only limited by the corresponding oscillation time τj=2π/ωj and, thus, is in the femtosecond range. A correlation analysis of these trajectories clearly separates the librational motions from the conformational dynamics of the solvation shells and yields the inhomogeneously broadened MIR spectra, if the theory of motional narrowing is properly included. The MIR spectrum of formaldehyde in solution obtained by TF-GV agrees very well with the FTTCF result, if one applies the so-called “harmonic approximation” quantum correction factor and a temperature scaling to the FTTCF intensities. Also for INMA an excellent agreement is achieved if one disregards a slight INMA overestimate of linewidths.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Fluorescence excitation spectroscopy of single chromophores in an amorphous polymer at low temperatures allows the study of single two-level systems (TLSs) of the matrix. With increasing temperature, more TLSs are thermally activated and contribute to random flipping, splitting, and/or broadening of single-molecule lines. In this paper we report on temperature-dependent changes of the intensity ratio between different components of single-molecule lines. The system under study is tetra-tert-butyl-terrylene in poly-isobutylene. Since the temperature dependent changes are due to thermal activation of individual TLSs, we could calculate the asymmetry of several of these TLSs yielding values between 0.25 and 1.5 meV. Some of the TLSs do not follow the Boltzmann activation law. [ABSTRACT FROM AUTHOR]

In this paper we examine the spectral moments of the absorption line shapes of aromatic- molecule·(rare gas)n heteroclusters to provide analytic expressions for the spectral shifts (δν), which are determined by the first moment, and for the homogeneous linewidths (Γ), which are determined by the central second moment (Δ) of the line shape. δν originates from the cumulative contributions of dispersive pair interactions, while Δ and Γ manifest the short-range dynamic nuclear fluctuations. Our analysis elucidates some of the general features of these spectroscopic observables, e.g., their dependence on the cluster structure and their size dependence, as well as some of their specific characteristics, e.g., their temperature dependence. We predict a weak temperature dependence of δν (=a+bT with b≪a/T) and a strong temperature dependence of Δ(∝T1/2), which is borne out by molecular dynamics (MD) simulations. We have derived cluster size equations (CSE) relating the spectroscopic observables of the finite cluster with those of the infinite bulk system. The excluded volume corrections for δν(n)∝n-1 and for Δ(n)∝n-3 are different, in accordance with the nonuniversability principle for CSEs. The predictions of the CSEs concur with experimental and MD simulation data for δν(n) and with MD simulation data for Δ(n). Finally, we have addressed dimensionality scaling of spectroscopic cluster properties, applicable for the situation of a common dimensionality (D≠3) for the cluster and for the infinite bulk. This analysis may be useful for the spectroscopic interrogation of doped clusters of low dimensionality, e.g., wire clusters (D=1) and planar clusters (D=2), as well as fractal clusters, e.g., clusters of porous materials. [ABSTRACT FROM AUTHOR]

A laser system composed of tunable lasers pumped by a copper vapor laser (Oxford Lasers Cu60) is described in this paper. The high resolution obtained with this system has allowed excitation of selective rotational levels of the 15 V and 10 V vibrational bands of the V 1B2 excited electronic state of the CS2 molecule in its vapor phase (∼100 mTorr). The rotational assignment of the excitation spectra was accomplished by observing the dispersed fluorescence. We show that it is not necessary to use a supersonic jet in order to assign the emission spectra of CS2. The goal of this work is to study the highly excited vibrational states of the ground electronic state of CS2 up to the first dissociation limit. For our purpose, there are two important consequences of the particular geometry of the 15 V excitation, which is just below and close to the bending potential barrier of the V 1B2 state. First, a very good Franck–Condon overlap in the excitation and a large Franck–Condon access to high vibrational states, as high as 20 000 cm-1, allow observation of the dispersed fluorescence through a high resolution monochromator with an OMA detector. This avoids the need for more complicated techniques, like SEP spectroscopy. Moreover, we show for the first time, that, in the V 1B2 excited state, a strong Coriolis interaction Q32 Q3 Jc couples the bending (0,3,0) and antisymmetric stretching levels (0,0,1). This breaking of the symmetric–antisymmetric selection rule gives access to the antisymetric stretching levels of the ground electronic state X Σ+g from the 15 V excitation. We also show that, below 12 000 cm-1, the vibrational couplings of CS2 can be described by a model of 2 degrees of freedom, which includes a strong 1:2 Fermi resonance and accidental resonant perturbations between adjacent polyads which is probably a first step in the transition to a chaotic regime in CS2. [ABSTRACT FROM AUTHOR]

Vibrational spectroscopy is increasingly used as a selective and sensitive probe of the interaction between a given molecule and its environment. For electrochemistry, in particular, vibrational spectroscopy has been useful in the process of sorting reactive intermediates and mechanisms out of the many possibilities which present themselves. In this paper we discuss a general approach to the analysis of environmental effects on molecular vibrations. The objective is to use vibrational spectroscopy to determine values of specific parameters in a set of intra- and intermolecular pair potentials. In the body of this paper, we discuss in detail how one can manipulate a variety of model potential energy functions in order to account for environmental effects. We then apply the method to the adsorption of tetrahedral molecules on a metal surface. We report infrared spectra for sulfate ion adsorbed on a platinum electrode, and we make use of our analysis of the spectra to suggest that the sulfate anion associates with the metal through only one oxygen atom. [ABSTRACT FROM AUTHOR]

In paper I, the theoretical TTOC and PTOC far-infrared absorption coefficients of diatomic polar molecules in rare-gas liquid have been expressed in terms of correlation functions of the Hamiltonian which describes the diatomic–medium interaction. In this paper these correlation functions are derived using a harmonic model for the liquid structure which takes into account some peculiarities such as dynamical behavior and geometrical arrangement of atoms in the liquid. The correlation functions and the different spectral contributions which appear in the spectral theory of paper I are numerically analyzed for a HCl–Ar solution. Comparison between theoretical and experimental spectra shows that the best agreement is obtained with the PTOC approach. [ABSTRACT FROM AUTHOR]

In this and the accompanying paper we present a theoretical treatment and experimental study, respectively, of the phenomenon termed purely rotational coherence. This phenomenon has been demonstrated to be useful as a time domain means by which to obtain high resolution spectroscopic information on excited state rotational levels of large molecules [Felker et al., J. Phys. Chem. 90, 724 (1986); Baskin et al., J. Chem. Phys. 84, 4708 (1986)]. Here, the manifestations in temporally resolved, polarization-analyzed fluorescence of coherently prepared rotational levels in samples of isolated symmetric and asymmetric top molecules are considered. These manifestations, for reasonably large molecules at rotational temperatures characteristic of jet-cooled samples, take the form of polarization-dependent transients and recurrences with temporal widths of the order of tens of picoseconds or less. The transients, which arise from the thermal averaging of many single molecule coherences, are examined with respect to their dependences on molecular parameters (rotational constants, transition dipole directions) and experimental parameters (polarization directions and temperature). A physical picture of rotational coherence as a reflection of the time-dependent orientation of molecules in the sample is developed. And, the influence of rotational coherence in experiments designed to probe intramolecular energy flow is discussed. In the accompanying paper, we present experimental results for jet-cooled t-stilbene and anthracene. For t-stilbene we determine rotational constants for vibrational levels in the S1 electronic state (from the recurrences) and we monitor the trends in rotational coherence vs vibrational coherence as the total energy in the molecule increases. [ABSTRACT FROM AUTHOR]

It is known that a new kind of large amplitude motion gives rise to as a very characteristic mode of weak chaos. This is essentially an unpredictable and intermittent motion taking place in a thin quasiseparatrix which wanders among several very clear vibrational modes. In this paper, we study the spectroscopic characterization of the quantum version of this large amplitude motion in terms of the dynamics of a wave packet, which is prepared in a narrow energy-range so that it is localized along a thin quasiseparatrix. In particular, we discuss possible significance of the weak chaos in single molecule spectroscopy, for which the spectra are supposed to be averaged neither in ensemble of molecules nor in time. That this wavepacket state is unusual originates from the extremely long-time behavior and the strong sensitivity to the initial condition at which the wave packet is prepared. The weak chaos combined with the statistical nature of quantum mechanics brings about a notion of unreproducibility in the spectrum. Conversely, it is anticipated that one of the distinguished features inherent to a single molecule spectroscopy manifests itself when weak chaos is observed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A benchmark study of the approximate approach to the optimal control of vibrational qubits, which was used in the original paper [J. Chem. Phys.126, 204102 (2007)], is presented. Two simplified assumptions are used in this method: A linear approximation for the dipole moment function and a harmonic approximation for the vibrational wave functions. Both assumptions are often used in spectroscopy and are known to work well for many molecules when the vibrational excitation is low. Here, we show that our method works well for the OH molecule, which exhibits a very anharmonic spectrum of vibrational eigenstates and a complicated dipole moment function. [ABSTRACT FROM AUTHOR]

A new approach is proposed to describe intermediate-to-strong linear vibronic coupling in an infinite molecular crystal. The Hamiltonian, transformed to the Lang–Firsov representation, is approximated by disregarding the terms involving more-than-two-particle excitations and block-diagonalized by the Fourier transformation. The spectroscopically relevant block corresponding to zero wave vector is further simplified by introducing a cutoff in the off-diagonal matrix elements and reduced to a manageable size by truncating the basis set, which enables one to diagonalize it numerically. The parametrization, based on independent experiments or theoretical estimates, is aimed to represent the sexithiophene crystal. The results, compared to those obtained for a finite cluster with equivalent material parameters, highlight the favorable convergence properties of the infinite-crystal approach. [ABSTRACT FROM AUTHOR]

Soft x-ray natural circular dichroism of amino acids is studied by means of ab initio methods. Several approaches to evaluate the oscillator and rotary strengths of core-to-valence excitations are compared from the viewpoint of basis set dependence: ground-state Hartree-Fock (HF) orbital set employed in (i) random phase approximation (RPA), (ii) static exchange approach (STEX) (unrelaxed), (iii) core-ionized state HF orbital set applied in STEX (relaxed), and (iv) HF excited state orbital set for each core-to-valence excited state. Furthermore in (i) the PRA in the framework of the density functional method (DFT) is compared with the RPA where the ab initio HF orbital set is used. In (iv), the oscillator and rotary strengths evaluated by different orbital sets for the initial and final states, namely, nonorthogonal ground-state and core-excited HF orbitals, are compared with those evaluated by using the core-excited HF orbital set to describe the initial (ground) state. It was shown that, among considered methods, the RPA provides most consistent and less time-consuming results for circular dichroism core excitation spectra. Discussion of the low energy part of K edge circular dichroism spectra of five common amino acids obtained with the help of RPA is presented. [ABSTRACT FROM AUTHOR]

The amide I vibrational circular dichroic response of alanine dipeptide analog (ADA) was theoretically investigated and the density functional theory calculation and fragment analysis results are presented. A variety of vibrational spectroscopic properties, local and normal mode frequencies, coupling constant, dipole, and rotational strengths, are calculated by varying two dihedral angles determining the three-dimensional ADA conformation. Considering two monopeptide fragments separately, we show that the amide I vibrational circular dichroism of the ADA can be quantitatively predicted. For several representative conformations of the model ADA, vibrational circular dichroism spectra are calculated by using both the density functional theory calculation and fragment analysis methods. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Vibrational Herzberg bands of the O[sub 2] molecule just below its first O(³P) + O(³P) dissociation limit are since long-known to be perturbed. Jenouvrier et al. [J. Mol. Spectrosc. 198, 136 (1999)] assigned the cause of the perturbations to five vibrational levels supported by the shallow minimum in the 1 ³Π[sub u], potential energy curve around 5.5a[sub 0]. Using ab initio potential energy curves and spin-orbit couplings from previous work [J. Chem. Phys. 116, 1954 (2002)] we present a full quantum calculation of all ungerade rotation-vibration-electronic states of oxygen just below the dissociation threshold, through a total angular momentum quantum number of J = 19. This calculation shows that the original assignment, based on a Hund's case (a) model of a regular 1 ³Π[sub u], multiplet was not correct. Based on our calculation we present a new assignment of the perturbing states: 1 ³Π[sub u,Ω=2](υ=0), 1 ³Π[sub u,1](0), 1 ³Π[sub u,2](1), 1 ³Π[sub u,1](1), and 1 ³Π[sub u,0[sup -]](0) in order of ascending term values. We show the new assignment to be consistent with experimental data and we also propose new spectroscopic parameters for the perturbing states. [ABSTRACT FROM AUTHOR]

In recent years, sum-frequency generation (SFG) has been used to investigate numerous interfaces including aqueous interfaces. A longstanding challenge to interpretation of the SFG results, along with the related aqueous-solution infrared and Raman spectra, is a lack of connection between features in the broad hydrogen-bonded region and molecular-level interactions or configurations. This paper reports results of a newly developed polarization analysis of the generated sum-frequency signal as a function of wavelength both to deconvolute spectral resonances and to characterize the dynamic polarization associated with the resonances. Operationally, the polarization angle of the generated sum frequency is determined by identifying the null angle. The technique is hence termed polarization-angle null analysis or PAN. PAN applied to ice is very powerful; it reveals that the hydrogen-bonded region of the basal face of ice Ih contains at least five oscillators, each with a distinct polarization. The dynamic polarizability of the longest wavelength oscillator is nearly entirely transverse (perpendicular to the surface normal, i.e., in the surface plane); in contrast, the shortest wavelength oscillator is almost entirely longitudinal (along the surface normal). [ABSTRACT FROM AUTHOR]

Assignments have been carried out for the 2ν3/(ν3+ν6)/2ν6 (triad)←ground state overtone bands and the triad←ν3/ν6 hot-band system of CHD3. A vibrational extrapolation method, using correspondences between a spherical-tensor formalism and the more conventional description of symmetric-rotor spectra, was used to facilitate the assignment and analysis of these bands. The resulting assignments have been confirmed by time-resolved double-resonance measurements. [ABSTRACT FROM AUTHOR]

This project was inspired by the widespread use of the properties of coated spheres in modeling the dielectric and spectroscopic behavior, including surface enhanced Raman spectroscopy, of a variety of dispersed systems. In this paper the self-polarizing contributions to the absorption and elastic scattering properties of a coated sphere are obtained in the large wavelength limit, or dipole approximation, in which the coating is treated as a polarizable, uniaxially anisotropic, shell with the local optic axis directed radially. Numerical calculations for CO on Ag are provided to illustrate some of the phenomena predicted by the equations. Of particular interest are the dependence of the absorption band for CO stretch upon particle size, surface coverage, and molecular orientation, and the dependence of the surface plasmon resonance absorption on particle size and coverage. Some limitations of the model are examined. [ABSTRACT FROM AUTHOR]

A model consisting in a quantum rigid rotor interacting with a quasiharmonic medium is presented to obtain the far-infrared spectra of diatomic polar molecules dissolved in rare-gas liquids. The absorption coefficient is calculated within the framework of two non-Markovian approaches called TTOC (total time ordered cumulants) and PTOC (partial time ordered cumulants). Both non-Markovian spectra contain the same correlation functions of the diatomic–medium interaction, which is expressed in terms of a Legendre polynomial series truncated up to second order. These correlation functions are calculated in paper II. The absorption cofficients appear as a sum of two spectral contributions. The first one, called secular contribution, is given as a juxtaposition of basic resonances, different in each of two non-Markovian approaches, associated to the absorption lines j→j+1. The second one, called interference contribution, takes into account the existence of a overlapping line effect. The contributions to the absorption coefficients from the P1 and P2 Legendre polynomials of the interaction are explicitly reported. [ABSTRACT FROM AUTHOR]

The homogeneous line shape of the infrared spectrum of a single molecule physisorbed on ionic substrates is determined on the basis of a renormalization technique of the total system Hamiltonian. The absorption profile can be written in terms of a limited cumulant series expansion of the dynamical couplings between the optical system formed by the vibration–orientation modes of the molecule, and the bath modes characterized by molecular translations and substrate phonons. The various causes of homogeneous broadening of the lines are studied, implying phase and population relaxations through intramolecular transfers. In this latter case, two situations are considered depending on whether the internal vibration modes of the admolecule are localized or resonant (quasi-resonant) with the substrate phonon modes. These situations are usual for small polyatomic molecules adsorbed on substrates with extended optical phonon bands. An application to the calculation of the Q*, P* and R* branch widths for CO, CO2 and NH3 molecules adsorbed on NaCl(001) and/or MgO(001) is extensively discussed. We show that, at low temperature T≲ 20 K, the homogeneous width is quite negligible and inhomogeneity must be invoked to interpret the measured width. By contrast, for increasing T values (T>= 50 K), homogeneous broadening increases and contributes significantly (about to 50%) to the measured width for CO and CO2 molecules adsorbed on clean substrates. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We propose a novel approach to cavity-ring-down-spectroscopy (CRDS) in which spectra acquired with a frequency-agile rapid-scanning (FARS) scheme, i.e., with a laser sideband stepped across the modes of a high-finesse cavity, are interleaved with one another by a sub-millisecond readjustment of the cavity length. This brings to time acquisitions below20 s for few-GHz-wide spectra composed of a very high number of spectral points, typically 3200. Thanks to the signal-to-noise ratio easily in excess of 10 000, each FARS-CRDS spectrum is shown to be sufficient to determine the line-centre frequency of a Doppler broadened line with a precision of 2 parts over 1011, thus very close to that of sub-Doppler regimes and in a few-seconds time scale. The referencing of the probe laser to a frequency comb provides absolute accuracy and long-term reproducibility to the spectrometer and makes it a powerful tool for precision spectroscopy and line-shape analysis. The experimental approach is discussed in detail together with experimental precision and accuracy tests on the (30 012) (00 001) P12e line of CO2 at ∼1.57 μm. [ABSTRACT FROM AUTHOR]

In two previous papers on the infrared emission spectra of gaseous BeH2, BeD2, and MgH2 molecules, we reported rotational analyses of the antisymmetric stretching fundamental band and several hot bands. The problems in the ℓ-type resonance fits of BeH2 and MgH2 have now been resolved, and the results are reported in this Note. [ABSTRACT FROM AUTHOR]

In two previous papers on the infrared emission spectra of gaseous BeH2, BeD2, and MgH2 molecules, we reported rotational analyses of the antisymmetric stretching fundamental band and several hot bands. The problems in the ℓ-type resonance fits of BeH2 and MgH2 have now been resolved, and the results are reported in this Note. [ABSTRACT FROM AUTHOR]

For computational rovibrational spectroscopy the choice of the frame is critical for an approximate separation of overall rotation from internal motions. To minimize the coupling between internal coordinates and rotation, Eckart proposed a condition [“Some studies concerning rotating axes and polyatomic molecules," Phys. Rev.47, 552–558 (1935)] and a frame that fulfills this condition is hence called an Eckart frame. A method is developed to introduce in a systematic way the Eckart frame for the expression of the kinetic energy operator (KEO) in the polyspherical approach. The computed energy levels of a water molecule are compared with those obtained using a KEO in the standard definition of the Body-fixed frame of the polyspherical approach. The KEO in the Eckart frame leads to a faster convergence especially for large J states and vibrationally excited states. To provide an example with more degrees of freedom, rotational states of the vibrational ground state of the trans nitrous acid (HONO) are also investigated. [ABSTRACT FROM AUTHOR]

Perturbation-facilitated two-color resonant four-wave-mixing spectroscopy is realized to access the (dark) triplet manifold of the C3 molecule from the singlet X1Σg+ ground state. The inherent nonlinear signal dependence and coherence of the technique result in a favorable detection of the excited triplet states of interest. The observation of a newly found 3Δu electronic state is achieved by a two-step excitation via 'gate-way' levels (i.e., singlet-triplet mixed levels). Additionally, by fixing the probe laser on a transition exhibiting mainly triplet-triplet character and scanning the pump laser, we demonstrate an effective spin-filtering in a four-wave mixing measurement where only transitions to the perturber 3Σu- state appear exclusively in an otherwise congested spectral range of the Comet band. Ab initio calculations of excited triplet states complement our analysis with the electronic assignment of the observed resonances. [ABSTRACT FROM AUTHOR]

We report a series of quantum-chemical calculations for the ground and some of the low-lying excited states of an isolated LiYb molecule by the spin-orbit multistate complete active space second-order perturbation theory (SO-MS-CASPT2). Potential energy curves, spectroscopic constants, and transition dipole moments (TDMs) at both spin-free and spin-orbit levels are obtained. Large spin-orbit effects especially in the TDMs of the molecular states dissociating to Yb(3P0,1,2) excited states are found. To ensure the reliability of our calculations, we test five types of incremental basis sets and study their effect on the equilibrium distance and dissociation energy of the ground state. We also compare CASPT2 and CCSD(T) results for the ground state spectroscopic constants at the spin-free relativistic level. The discrepancies between the CASPT2 and CCSD(T) results are only 0.01 Å in equilibrium bond distance (Re) and 200 cm-1 in dissociation energy (De). Our CASPT2 calculation in the supermolecular state (R=100 a.u.) with the largest basis set reproduces experimental atomic excitation energies within 3% error. Transition dipole moments of the super molecular state (R=100 a.u.) dissociating to Li(2P) excited states are quite close to experimental atomic TDMs as compared to the Yb(3P) and Yb(1P) excited states. The information obtained from this work would be useful for ultracold photoassociation experiments on LiYb. [ABSTRACT FROM AUTHOR]

Parity violation (PV) effects to the electronic ground state structure for a series of chiral tungsten molecules of the type NWXYZ (X, Y, Z=H, F, Cl, Br, or I) are compared using four- (Dirac) and two- (X2C) component relativistic Hartree–Fock and density functional theories. The results show the computationally more affordable two-component X2C approach yields accurate results for all molecules investigated. The PV energy differences between the two enantiomers range from as little as 0.4 Hz for NWClBrI to 140 Hz for NWHClI using a generalized gradient approximation including exact exchange (B3LYP). The W[Single_Bond]N stretching mode in these molecules lies in the experimentally favorable CO2 laser frequency range, and we therefore investigated PV effects in vibrational transitions using a single normal mode analysis. Here the PV frequency shift between the two enantiomers ranges from 1.6 mHz for NWFBrI to 710 mHz for NWHClI. Thus these types of molecules could be useful for the future detection of PV effects in chiral molecules. [ABSTRACT FROM AUTHOR]

The electronic structure of single and multiple layers of C60 molecules deposited on a Rh(100) surface is investigated by means of valence photoemission spectroscopy and density functional theory calculations. The binding of the fullerene monolayer to the metal surface yields the appearance of a new state in the valence band spectrum crossing the Fermi level. Insight into the metallization of the metal/fullerene interface is provided by the calculated electronic structure that allows us to correlate the measured interface state with a strong hybridization between the Rh metal states and the highest and lowest molecular orbitals. This results in a net charge transfer of ≈0.5e–0.6e from the metal to the p states of the interfacial C atoms. The charge transfer is shown to be very short range, involving only the C atoms bound to the metal. The electronic structure of the second C60 layer is already insulating and resembles the one measured for C60 multilayers supported by the same substrate or calculated for fullerenes isolated in vacuum. The discussion of the results in the context of other C60/metal systems highlights the distinctive electronic properties of the molecule/metal interface determined by the Rh support. [ABSTRACT FROM AUTHOR]

We report the first measurement of the spectrum of the NO–N2 complex in the region of the first vibrational NO overtone transition. The origin band of the complex is blueshifted by 0.30 cm-1 from the corresponding NO monomer frequency. The observed spectrum consists of three bands assigned to the origin band, the excitation of one quantum of z-axis rotation and one associated hot band. The spacing of the bands and the rotational structure indicate a T-shaped vibrationally averaged structure with the NO molecule forming the top of the T. These findings are confirmed by high level ab initio calculations of the potential energy surfaces in planar symmetry. The deepest minimum is found for a T-shaped geometry on the A″-surface. As a result the sum potential also has the global minimum for this structure. The different potential surfaces show several additional local minima at slightly higher energies indicating that the complex most likely will perform large amplitude motion even in its ground vibrational state. Nevertheless, as suggested by the measured spectra, the complex must, on average, spend a substantial amount of time near the T-shaped configuration. [ABSTRACT FROM AUTHOR]

The ability of coupled-cluster models to predict vertical excitation energies is tested on the electronic states of carbon-chain radicals of particular relevance to interstellar chemistry. Using spin-unrestricted and -restricted reference wave functions, the coupled-cluster singles and doubles (CCSD) model and a triples-including model (CC3) are tested on the σ radicals C2H and C4H. Both molecules exhibit low-lying excited states with significant double-excitation character (as well as states of quartet multiplicity) and are thus challenging cases for excited-state approaches. In addition, we employ two diagnostics for the reliability of the CC results: the approximate excitation level (AEL) relative to the ground state and the difference between excitation energies obtained with spin-unrestricted and spin-restricted reference wave functions (the U-R difference). We find that CCSD yields poor excitation energies for states with AEL significantly larger than ca. 1.1 and/or large U-R differences, as well as for certain states exhibiting large spin contamination or other inadequacies in the reference determinant. In such cases, connected triple excitations can be included in the model and generally provide improved results. Furthermore, we find that large discrepancies exist between CC and multireference (MR) results for certain states. These disagreements are not related to basis-set effects, but likely arise from the lack of spin adaptation in conventional spin-orbital CC implementations and active space selection in the MR models. [ABSTRACT FROM AUTHOR]

The collision-induced rototranslational hyper-Rayleigh spectra of gaseous H2–He mixture are computed and discussed in the binary regime. As the input data we use our ab initio computed H2–He collision-induced first dipole hyperpolarizability tensor Δβ(R). Both the vector and the septor part of the H2–He hyper-Rayleigh spectra are evaluated at room temperature (T=295 K). The spectra are calculated assuming the full quantum computations based on the Schrödinger equation of the relative translational motion in the isotropic H2–He potential as well as using semiclassical methods. [ABSTRACT FROM AUTHOR]

We construct the Kohn–Sham density response function χ0 in a previously described basis of the space of orbital products. The calculational complexity of our construction is O(N2Nω) for a molecule of N atoms and in a spectroscopic window of Nω frequency points. As a first application, we use χ0 to calculate the molecular spectra from the Petersilka–Gossmann–Gross equation. With χ0 as input, we obtain the correct spectra with an extra computational effort that grows also as O(N2Nω) and, therefore, less steeply in N than the O(N3) complexity of solving Casida’s equations. Our construction should be useful for the study of excitons in molecular physics and in related areas where χ0 is a crucial ingredient. [ABSTRACT FROM AUTHOR]

Oxidation reactions of the gas-phase titanium atom in its excited state with oxygen molecule, Ti(a5FJ)+O2→TiO(A3[uppercase_phi_synonym],B3Π)+O, were studied by a crossed-beam technique. Metastable excited Ti, Ti(a5FJ), was generated by an optical pumping method and the reaction products were detected by the chemiluminescence spectroscopy. The chemiluminescence from TiO(A3[uppercase_phi_synonym],B3Π) was analyzed to determine vib-rotational state distributions of both excited states and their branching ratio. The vib-rotational state distribution of TiO(B) was represented by the statistical energy disposal and the branching ratio of TiO(A)/TiO(B) was also consistent with the statistical expectation. These results suggested the presence of long-lived intermediates in the course of the reactions of the excited Ti(a5FJ) atom with O2. Also observed was the significant deviation of the vibrational state distribution of TiO(A) from the statistical one and another reaction pathway which may not proceed via the long-lived intermediates was implied. [ABSTRACT FROM AUTHOR]

We analyze the validity of the commonly used electric-field (E-field) approximation to vibrational OH stretch Raman spectra of dilute HOD in D2O by computing the OH stretch frequency of all molecules in several different structure models, each containing around 2000 molecules. The calculations are done at the B3LYP level using clusters containing 32 molecules centered around the molecule for which the frequencies are calculated; the large cluster size is required due to significant nonlocal contributions influencing the computed frequencies. The vibrational frequencies are determined using a six-point potential optimized discrete variable representation. Raman and infrared intensities are furthermore computed to generate the spectra. We find that a quadratic fit of E-field versus frequency gives a reasonable representation of the calculated distribution of frequencies. However, the mapping depends significantly on the structural model and is thus not universal. Anharmonic couplings are calculated for several optimized clusters showing a general trend to compress the computed frequency distributions, which is in agreement with dynamical simulations (motional narrowing). [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and time-dependent DFT calculations have been performed to investigate the Raman scattering spectra of metal-molecule complex and metal-molecule-metal junction architectures interconnected with 4-aminothiophenol (PATP) molecule. The simulated profiles of normal Raman scattering (NRS) spectra for the two complexes (Ag2-PATP and PATP-Au2) and the two junctions (Ag2-PATP-Au2 and Au2-PATP-Ag2) are similar to each other, but exhibit obviously different Raman intensities. Due to the lager static polarizabilities of the two junctions, which directly influence the ground state chemical enhancement in NRS spectra, the calculated normal Raman intensities of them are stronger than those of two complexes by the factor of 102. We calculate preresonance Raman scattering (RRS) spectra with incident light at 1064 nm, which is much lower than the S1 electronic transition energy of complexes and junctions. Ag2-PATP-Au2 and Au2-PATP-Ag2 junctions yield higher Raman intensities than those of Ag2-PATP and PATP-Au2 complexes, especially for b2 modes. This effect is mainly attributed to charge transfer (CT) between the metal gap and the PAPT molecule which results in the occurrence of CT resonance enhancement. The calculated pre-RRS spectra strongly depend on the electronic transition state produced by new structures. With excitation at 514.5 nm, the calculated pre-RRS spectra of two complexes and two junctions are stronger than those of with excitation at 1064 nm. A charge difference densities methodology has been used to visually describe chemical enhancement mechanism of RRS spectrum. This methodology aims at visualizing intermolecular CT which provides direct evidence of the Herzberg–Teller mechanism. [ABSTRACT FROM AUTHOR]

Complex χ(2) spectra of air/water interfaces in the presence of charged surfactants were measured by heterodyne-detected broadband vibrational sum frequency generation spectroscopy for the first time. In contrast to the neat water surface, the signs of χ(2) for two broad OH bands are the same in the presence of the charged surfactants. The obtained χ(2) spectra clearly showed flip-flop of the interfacial water molecules which is induced by the opposite charge of the head group of the surfactants. With the sign of β(2) theoretically obtained, the absolute orientation, i.e., up/down orientation, of water molecules at the charged aqueous surfaces was uniquely determined by the relation between the sign of χ(2) and the molecular orientation angle. Water molecules orient with their hydrogen up at the negatively charged aqueous interface whereas their oxygen up at the positively charged aqueous interface. [ABSTRACT FROM AUTHOR]

Recent development in single molecule spectroscopy enabled us to measure the decay kinetics of individual excited probes surrounded by randomly distributed quenchers. Since the distribution of quenchers around individual excited probes change from one excited probe to another, the quenching rate constant also changes from one excited probe to another. We calculated the distribution of quenching rate constants of individual excited probes theoretically and analyzed the observed distributions of quenching rate constants, which were recently measured by Lupton et al. [J. Phys. Chem. C 111, 11511 (2007)] by using single molecule spectroscopy. [ABSTRACT FROM AUTHOR]

A pulse sequence, IDEAL-II, is proposed based on the concept of intermolecular dipolar-interaction enhanced all lines [Z. Chen et al., J. Am. Chem. Soc. 126, 446 (2004)] for obtaining one-dimensional (1D) high-resolution liquid NMR spectra in inhomogeneous fields via two-dimensional acquisitions. With the new acquisition scheme, the range of magnetic field inhomogeneity rather than chemical shift is sampled in the indirect dimension. This enables a great reduction in acquisition time and amount of data, much improved over the original IDEAL implementation. It is applicable to both isolated and J-coupled spin systems in liquid. For the latter, apparent J coupling constants are magnified threefold in spectra obtained with this sequence. This allows a more accurate measurement of J coupling constants in the cases of small J coupling constants or large inhomogeneous fields. Analytical expression was derived based on intermolecular multiple-quantum coherence treatments. Solution samples that were purposely deshimmed and biological samples with intrinsic field inhomogeneities were tested. Experimental results demonstrate that this sequence retains useful structural information including chemical shifts, relative peak areas, and multiplet patterns of J coupling even when the field inhomogeneity is severe enough to almost erase all spectroscopic information with conventional 1D single-quantum coherence techniques. This sequence is more applicable to weakly coupled and uncoupled spin systems, potentially useful for studying metabolites in in vivo NMR spectroscopy and for characterizing technologically important new materials in combinatorial chemistry. [ABSTRACT FROM AUTHOR]

We study the power spectrum of a random telegraphic noise with the distribution density of waiting times τ given by ψ(τ)∝1/τμ, with μ≈2. The condition μ<2 violates the ergodic hypothesis, and in this case the adoption of Wiener–Khintchine (WK) theorem for the spectrum evaluation requires some caution. We study this problem theoretically and numerically and we prove that the power spectrum obeys the prescription S(f)=K/fη, with η=3-μ, namely, the 1/f noise lives at border between the ergodic μ>2 and nonergodic μ<2 condition. We study sequences with the finite length L. In the case μ<2 the adoption of WK theorem is made legitimate by two different kinds of truncation effects: the physical and observation-induced effect. In the former case ψ(τ) is truncated at τ≈Tmax and L>Tmax ensures the condition of interrupted aging. In this case, we find that K is a number independent of L. The latter case, L≤Tmax, is more challenging. It was already solved by Margolin and Barkai, who used time asymptotic arguments based on the ergodicity breakdown and obtained K∝1/L2-μ, proving that the out-of-equilibrium nature of the condition μ<2 is signaled by the decrease of K with the increase of L. We use a generalized version of the Onsager principle that leads us to the same conclusion from a somewhat more extended view valid also for the transient out-of-equilibrium case of μ>2. We do not limit our treatment to the time asymptotic case, thereby producing a prediction that accounts for the transition from the 1/fη to the 1/f2 regime, recently observed in an experiment on blinking quantum dots. Our theoretical approach allows us to discuss some other recent experiments on molecular intermittent fluorescence and affords indications that should help to assess whether the spectrum is determined by the L≤Tmax or by the L≥Tmax condition. [ABSTRACT FROM AUTHOR]

Rotational spectra of small-sized (H2)N-OCS clusters with N=2–7 were measured using a pulsed-jet Fourier transform microwave spectrometer. These include spectra of pure (para-H2)N-OCS clusters, pure (ortho-H2)N-OCS clusters, and mixed ortho-H2 and para-H2 containing clusters. The rotational lines of ortho-H2 molecules containing clusters show proton spin-proton spin hyperfine structure, and the pattern evolves as the number of ortho-H2 molecules in the cluster increases. Various isotopologues of the clusters were investigated, including those with O13CS, OC33S, OC34S, and O13C34S. Nuclear quadrupole hyperfine structures of rotational transitions were observed for 33S (nuclear spin quantum number I=3/2) containing isotopologues. The 33S nuclear quadrupole coupling constants are compared to the corresponding constant of the OCS monomer and those of the HeN-OCS clusters. The assignment of the number of solvating hydrogen molecules N is supported by the analyses of the proton spin-proton spin hyperfine structures of the mixed clusters, the dependence of line intensities on sample conditions (pressure and concentrations), and the agreement of the (para-H2)N-OCS and (ortho-H2)N-OCS rotational constants with those from a previous infrared study [J. Tang and A. R. W. McKellar, J. Chem. Phys. 121, 3087 (2004)]. [ABSTRACT FROM AUTHOR]

A methodology for calculating the temperature-dependent magnetic circular dichroism (MCD) of open-shell molecules with time-dependent density functional theory (TDDFT) is described. The equations for the MCD of an open-shell molecule including spin-orbit coupling in the low- and high-temperature limits are reviewed. Two effects lead to the temperature-dependent MCD: the breaking of degeneracies and the perturbation of transition dipoles by spin-orbit coupling. The equations necessary to evaluate the required terms using TDDFT-derived quantities are presented. The performance of the formalism is demonstrated through application to the MCD of several molecules. The spectra of these molecules have differing properties with respect to bandwidth, temperature dependence of the MCD, and relative magnitude of the temperature-dependent and temperature-independent components of the MCD. The important features of the experimental spectra are reproduced by the calculations. [ABSTRACT FROM AUTHOR]

The rotational spectra of C3N-, C4H-, and C4D- have been measured at high-spectral resolution by Fourier transform microwave spectroscopy. For both C3N- and C4D-, hyperfine structure in the lowest-J transitions has been resolved and measured to better than 0.1 ppm. The quadrupole coupling constants eQq for both anions are close to those of the neutral counterparts C3N and C4D, and that of C3N- is in good agreement with theoretical calculations. Several properties of these anions, including their linewidths, drift velocities, and abundances, are systematically compared to similar-sized neutral molecules. The production of C4H- with different hydrocarbon precursor and buffer gases is also discussed. [ABSTRACT FROM AUTHOR]

An exactly solvable lattice model describing a binary solution is considered where rodlike molecules of types AA and BB cover the links of a honeycomb lattice, the neighboring molecular ends having three-body and orientation-dependent bonding interactions. At phase coexistence of AA-rich and BB-rich phases, the average fraction of each type of triangle of neighboring molecular ends is calculated exactly. The fractions of the different types of triangles are then used to deduce the local microscopic structure of the coexisting phases for a case of the model that contains two closed loops in the phase diagram. [ABSTRACT FROM AUTHOR]