The 1 3A′ HCN and 1 3A′ HCO+ Vibrational Frequencies and Spectroscopic Constants from Quartic Force Fields

The Journal of Physical Chemistry A
Building on previous studies involving coupled cluster quartic force fields for the description of spectroscopic constants and vibrational frequencies of astronomically relevant molecules, this work applies the same techniques to the elucidation of such properties for the bent 1 3A′ state of HCN and the isoelectronic 1 3A′ HCO+. Core correlation is treated both by explicit means and as a correction. Each approach gives closely comparable spectroscopic constants and vibrational frequencies once more, indicating that the composite method is a viable and less costly alternative. We are providing fundamental vibrational frequencies for these systems where agreement with experiment in previous studies has been within 4 cm–1 or better. Frequencies for the first overtones and combination bands as well as various spectroscopic constants are also reported.Read more

Orientational Time Correlation Functions for Vibrational Sum-Frequency Generation. 1. Acetonitrile

The Journal of Physical Chemistry A
Orientational time correlation functions (TCFs) are derived for vibrational sum-frequency generation (VSFG) spectroscopy of the symmetric and asymmetric stretches of high-symmetry oscillators such as freely rotating methyl groups, acetylenic C–H groups, and cyanide groups. Molecular dynamics simulations are used to calculate these TCFs and the corresponding elements of the second-order response for acetonitrile at the liquid/vapor and liquid/silica interfaces. We find that the influence of reorientation depends significantly on both the functional group in question and the polarization conditions used. Additionally, under some circumstances, reorientation can cause the VSFG response function to grow with time, partially counteracting the effects of other dephasing mechanisms.Read more