Infrared spectroscopy of HOOO and DOOO in ~4He nanodroplets

摘要

The HOOO hydridotrioxygen radical and its deuterated analog (DOOO) have been isolated in helium nanodroplets following the in situ association reaction between OH and O_2. The infrared spectrum in the 3500-3700 cm~(?1) region reveals bands that are assigned to the ν_1 (OH stretch) fundamental and ν_1 + ν_6 (OH stretch plus torsion) combination band of the trans-HOOO isomer. The helium droplet spectrum is assigned on the basis of a detailed comparison to the infrared spectrum of HOOO produced in the gas phase [E. L. Derro, T. D. Sechler, C. Murray, and M. I. Lester, J. Chem. Phys. 128, 244313 (2008)]. Despite the characteristic low temperature and rapid cooling of helium nanodroplets, there is no evidence for the formation of a weakly bound OH-O_2 van der Waals complex, which implies the absence of a kinetically significant barrier in the entrance channel of the reaction. There is also no spectroscopic evidence for the formation of cis-HOOO, which is predicted by theory to be nearly isoenergetic to the trans isomer. Under conditions that favor the introduction of multiple O_2 molecules to the droplets, bands associated with larger H/DOOO-(O_2)_n clusters are observed shifted ～1-10 cm~(?1) to the red of the trans-H/DOOO ν_1 bands.