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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]

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]

Angle-resolved photoelectron spectra from rotationally selected à 1Au state acetylene have been recorded using velocity-map imaging. Several Renner-Teller split vibrational bands have been observed and assigned, showing good agreement with previous zero kinetic energy photoelectron (ZEKE) work [S. T. Pratt, P. M. Dehmer, and J. L. Dehmer, J. Chem. Phys. 99, 6233 (1993); S.-J. Tang, Y.-C. Chou, J. J.-M. Lin, and Y.-C. Hsu, ibid. 125, 133201 (2006).] The extracted photoelectron angular distributions (PADs) corresponding to these bands show a strong dependence on the vibronic angular momentum projection quantum number K+. Subbands with odd K+ show PADs with maximum intensity along the polarization vector of the ionizing laser beam, while those with even K+ show PADs with maximum intensity perpendicular to this direction. Velocity-map images recorded at low photoelectron energies approach rotational resolution of the ion, and the evolution of the PADs with increasing rotational level prepared in the à 1Au state indicates the potential of a “complete” determination of the photoionization dynamics of the à 1Au state. This is further investigated in the following paper. [ABSTRACT FROM AUTHOR]

X-ray and neutron diffractions, vibrational spectroscopy, and x-ray Raman scattering and absorption experiments on water are often interpreted in terms of hydrogen bonding. To this end a number of geometric definitions of hydrogen bonding in water have been developed. While all definitions of hydrogen bonding are to some extent arbitrary, those involving one distance and one angle for a given water dimer are unnecessarily so. In this paper the authors develop a systematic procedure based on two-dimensional potentials of mean force for defining cutoffs for a given pair of distance and angular coordinates. They also develop an electronic structure-based definition of hydrogen bonding in liquid water, related to the electronic occupancy of the antibonding OH orbitals. This definition turns out to be reasonably compatible with one of the distance-angle geometric definitions. These two definitions lead to an estimate of the number of hydrogen bonds per molecule in liquid simple point charge/extended (SPC/E) water of between 3.2 and 3.4. They also used these and other hydrogen-bond definitions to examine the dynamics of local hydrogen-bond number fluctuations, finding an approximate long-time decay constant for SPC/E water of between 0.8 and 0.9 ps, which corresponds to the time scale for local structural relaxation. [ABSTRACT FROM AUTHOR]

A continuous wave distributed feedback diode laser operating in the near infrared at wavelengths close to 1650 nm has been used to measure the extinction of light by single aerosol particles. The technique of optical feedback cavity ring-down spectroscopy (CRDS) was used for measurement of CRDS events at a repetition rate of 1.25 kHz. This very high repetition rate enabled multiple measurements of the extinction of light by single aerosol particles for the first time and demonstrated the dependence of light scattering on the position of a particle within the laser beam. A model is proposed to explain quantitatively this phenomenon. The minimum detectable dimensionless extinction coefficient [variant_greek_epsilon]min was determined to be 3×10-6. Extinction values obtained for single spherical polymer beads from a monodisperse sample of particles of diameter of 4 μm are in near-quantitative agreement with the values calculated by the Mie scattering theory. The deviations from the Mie theory expected for measurement of extinction by CRDS using a continuous wave laser are discussed in the companion paper. [ABSTRACT FROM AUTHOR]

We present several numerical applications based upon the effective-mode formulation for the short-time dynamics through conical intersections in macrosystems, as detailed in the preceding paper and first proposed by Cederbaum et al. [Phys. Rev. Lett. 94, 113003 (2005)]. The macrosystem, containing a vast number of nuclear degrees of freedom (modes), is decomposed into a system part and an environment part. Only three effective environmental modes are needed—together with the system’s modes—to accurately calculate the low resolution spectra and the short-time dynamics of the entire macrosystem. For the systems discussed here, results are compared to those of a full quantum wave-packet propagation. Some rules are extracted to provide general tendencies; these rules allow one to understand and predict the dynamical properties in more general situations where the exact quantum dynamics of the macrosystem is out of reach. [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]

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]

All the pure rotational transitions reported in the previous studies [J. Chem. Phys. 113, 10121 (2000); J. Mol. Spectrosc. 222, 22 (2003)] and newly observed rotation-vibration transitions, P=1/2←3/2, for Ar–SH and Ar–SD [J. Chem. Phys. (2005), the preceding paper] have been simultaneously analyzed to determine a new intermolecular potential-energy surface of Ar–SH in the ground state. A Schrödinger equation considering the three-dimensional freedom of motion for an atom-diatom complex in the Jacobi coordinate, R, θ, and r, was numerically solved to obtain energies of the rovibrational levels using the discrete variable representation method. A three-dimensional potential-energy surface is determined by a least-squares fitting with initial values of the parameters for the potential obtained by ab initio calculations at the RCCSD(T)/aug-cc-pVTZ level of theory. The potential well reproduces all the observed data in the microwave and millimeter wave regions with parity doublings and hyperfine splittings. Several low-lying rovibrational energies are calculated using the new potential-energy surface. The dependence of the interaction energy between Ar and SH(2Πi) on the bond length of the SH monomer is discussed. [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]

This paper presents an exact solution for the free energy of linear solvation of a dipolar solute in an arbitrary dielectric material with a microscopic spectrum of polarization fluctuations. The solution is given in terms of wave vector-dependent longitudinal and transverse structure factors of the polarization fluctuations in the pure dielectric. Good agreement with computer simulations of dipole solvation in dipolar and dipolar–quadrupolar liquids is achieved. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]