PAUL L. RASTON, TAO LIANG, EMMANUEL I. OBI AND GARY E. DOUBERLY, Department of Chemistry, University of Georgia, Athens, Georgia 30602, USA.
The vinyl radical has been trapped in 4He nanodroplets and probed with infrared laser spectroscopy in the CH stretch region between 2850 and 3200 cm-1. The assigned band origins for the CH2 symmetric ( 3), CH2 antisymmetric ( 2), and lone -CH stretch ( 1) vibrations are in good agreement with previously reported full-dimensional vibrational configuration interaction calculations. For all three bands, a -type and 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 and high-resolution jet-cooled infrared spectra reveal that the effect of the 4He solvent is to reduce the ground and 3 excited state tunneling splittings by ~20%. This solvent-induced modification of the tunneling dynamics can be reasonably accounted for by assuming either an ~2.5% increase in the effective barrier height along the tunneling coordinate or an ~5% increase in the effective reduced mass of the tunneling particles.