15min:

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.