The geometrical structures and electronic and vibrational spectra of silicon clusters with 20, 60, and 70 atoms are investigated. Using a first-principles quantum-molecular-dynamics method we obtain the equilibrium structures, and study the effects of an exciton-induced lattice relaxation in these systems. The relaxation induced by the exciton may result in a strong distortion of metastable str...

Slow photoelectron velocity-map imaging (SEVI) spectroscopy has been used to study the vibronic structure of gas-phase α- and β-naphthyl radicals (C(10)H(7)). SEVI of cryogenically cooled anions yields spectra with <4 cm(-1) resolution, allowing for the observation and interpretation of congested vibrational structure. Isomer-specific photoelectron spectra of detachment to the radical ground el...

It is widely believed that the addition of salts to water engenders structural changes in the hydrogen-bond network well beyond the adjacent shell of solvating molecules. Classification of many ions as "structure makers" and "structure breakers" has been based in part on corresponding changes in the vibrational spectra (Raman and IR). Here we show that changes in O-H vibrational spectra induced...

Predissociation spectra in the 2.6-3.3 μm region were observed for protonated chlorine nitrate and protonated nitric acid as well as some of their isotopomers (HXNO3, X ) H, D, 35Cl, 37Cl). Two protonated isomers of both ClONO2 and HNO3 were identified from the vibrational spectra. The lowest energy isomer was the ion-molecule complex NO2(HOX) formed by protonation of the XO group. The second i...

Oligomers of the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride, C(24)H(8)O(6) (PTCDA) are studied by means of helium nanodroplet isolation spectroscopy. In contrast to the monomer absorption spectrum, which exhibits clearly separated, very sharp absorption lines, it is found that the oligomer spectrum consists of three main peaks having an apparent width orders of magnitud...

The neutron powder diffraction and inelastic neutron scattering (INS) spectra of the electron donor-acceptor complex, tetracyanoethylene-hexamethylbenzene have been studied as a function of pressure to 0.414 GPa. Using the PW91 and PBE density functional theories, the unit cell vectors were calculated as a function of pressure and are compared to those experimentally obtained from the diffracti...

Quantum chemical calculations have been performed to compute optimized molecular geometry, atomic charges and vibrational characteristics for 2-hydroxy-3-methoxy-N-(2-chloro-benzyl)-benzaldehyde-imine (C15H14O2NCl) in the ground state using restricted Hartree-Fock (RHF) and density functional theory (DFT) methods with 6-31+G** basis set. NBO analysis is also performed. The IR and Raman spectra ...

Vibrationally resolved spectra provide a stringent test of the accuracy of theoretical calculations. We combine the thawed Gaussian approximation (TGA) with an on-the-fly ab initio (OTF-AI) scheme to calculate the vibrationally resolved emission spectra of oligothiophenes with up to five rings. The efficiency of the OTF-AI-TGA permits treating all vibrational degrees of freedom on an equal foot...

Monitoring reaction paths is not only a fundamental scientific issue but also helps us to understand and optimize the catalytic process. Infrared (IR) and Raman spectroscopies are powerful tools for detecting particular molecules or intermediate products as a result of their ability to provide the molecular "finger-print". However, theoretical modeling for the vibrational spectra of molecular a...

Gas phase vibrational spectra of BrHI- and BrDI- have been measured from 6 to 17 microm (590-1666 cm(-1)) using tunable infrared radiation from the free electron laser for infrared experiments in order to characterize the strong hydrogen bond in these species. BrHI-.Ar and BrDI-.Ar complexes were produced and mass selected, and the depletion of their signal due to vibrational predissociation wa...