The ethyl radical in superfluid helium nanodroplets: Rovibrational spectroscopy and ab initio computations

摘要

The ethyl radical has been isolated and spectroscopically characterized in ~4He nanodroplets. The band origins of the five CH stretch fundamentals are shifted by < 2 cm~(-1) from those reported for the gas phase species [S. Davis, D. Uy, and D. J. Nesbitt, J. Chem. Phys. 112, 1823 (2000)10.1063/1.480746; T. H?ber, A. C. Blair, D. J. Nesbitt, and M. D. Schuder, J. Chem. Phys. 124, 054316 (2006)10.1063/1.2140740]. The symmetric CH_2 stretching band (v_1) is rotationally resolved, revealing nuclear spin statistical weights predicted by G12 permutation-inversion group theory. A permanent electric dipole moment of 0.28 (2) D is obtained via the Stark spectrum of the v_1 band. The four other CH stretch fundamental bands are significantly broadened in He droplets and lack rotational fine structure. This broadening is attributed to symmetry dependent vibration-to-vibration relaxation facilitated by the He droplet environment. In addition to the five fundamentals, three a_1′ overtone/combination bands are observed, and each of these have resolved rotational substructure. These are assigned to the 2v_(12), v _4 + v_6, and 2v_6 bands through comparisons to anharmonic frequency computations at the CCSD(T)/cc-pVTZ level of theory.