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

The ethyl radical has been isolated and spectroscopically characterized in He-4 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); T. Haber, A. C. Blair, D. J. Nesbitt, and M. D. Schuder, J. Chem. Phys. 124, 054316 (2006)]. The symmetric CH2 stretching band (v(1)) is rotationally resolved, revealing nuclear spin statistical weights predicted by G(12) permutation-inversion group theory. A permanent electric dipole moment of 0.28 (2) D is obtained via the Stark spectrum of the v1 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. (C) 2013 AIP Publishing LLC.