INRARED SPECTROSCOPY AND TUNNELING DYNAMICS OF THE VINYL RADICAL IN $^{4}$He NANODROPLETS

Abstract

The vinyl radical has been trapped in $^{4}$He nanodroplets and probed with infrared laser spectroscopy in the CH stretch region between 2850 and 3200 cm$^{-1}$. The assigned band origins for the CH${_2}$ symmetric ($\nu$${_3}$), CH${_2}$ antisymmetric ($\nu$${_2}$), and lone $\alpha$-CH stretch ($\nu$${_1}$) vibrations are in good agreement with previously reported full-dimensional vibrational configuration interaction calculations., 174301 2009} For all three bands, $\textit{a}$-type and $\textit{b}$-type transitions are observed from the lowest symmetry allowed roconvibrational state of each nuclear spin isomer, which allows for a determination of the tunneling splittings in both the ground and excited vibrational levels. Comparisons to gas phase millimeter-wave rotation-tunneling, 3604 2004} and high-resolution jet-cooled infrared spectra, 044305 (2008)} reveal that the effect of the $^{4}$He solvent is to reduce the ground and $\nu$${_3}$ excited state tunneling splittings by $\approx$20\%. This solvent-induced modification of the tunneling dynamics can be reasonably accounted for by assuming either an $\approx$2.5\% increase in the effective barrier height along the tunneling coordinate or an $\approx$5\% increase in the effective reduced mass of the tunneling particles.