Photodesorption efficiency of OH radical on the ice surface in the wavelength range from ultraviolet to visible

TL;DR

This study measures the photodesorption efficiency of OH radicals from water ice across 310-700 nm, revealing wavelength-dependent behaviors and mechanisms involving bound and weakly bound OH radicals.

Contribution

First measurement of OH radical photodesorption efficiencies from ice in the visible range, showing a one-photon process and binding-dependent desorption.

Findings

Photodesorption occurs via a one-photon process across the entire visible spectrum.

Efficiency depends strongly on wavelength and binding strength of OH radicals.

Both weakly and strongly bound OH radicals are desorbed at shorter wavelengths.

Abstract

The photodesorption efficiencies of the hydroxyl (OH) radical from the water ice surface were measured in the range of 310-700 nm for the first time. Although isolated H$_2$O molecules and OH radicals do not absorb visible photons, the photodesorption of OH interacting with the ice surface was found to occur by a one-photon process in the entire visible range. The photodesorption efficiency strongly depended on the wavelength, and the analyses of photodesorption cross sections indicated that only strongly bound OH radicals were desorbed at longer wavelengths, whereas both weakly and strongly bound OH radicals were desorbed at shorter wavelengths.