Infrared spectroscopy of HOOO and DOOO in 4He nanodroplets

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.