High-resolution inner-shell photoabsorption of the OH and OD free radicals

Abstract

The O 1s photoabsorption (ion-yield) spectra of OH (2Πi,v″=0) and OD (2Πi,v″=0) radicals have been studied in the gas phase for the first time. Spectroscopic parameters for the O 1s→π excited Σ+2 state of OH and OD, observed at ∼525.8 eV, have been obtained from a Franck–Condon analysis comparing the spectra of both molecules. The lifetime width of this state has been measured as Γ=147±11 meV and Γ=156±7 meV for OH and OD, respectively. Excellent quantitative agreement is found between the experimental spectroscopic parameters re, ωe, and T0, measured in this work for the Σ+2 state and recent theoretical results obtained for OH by high-level ab initio calculations. The spectroscopic parameters predicted by the equivalent-core model are close to the experimental values within a few percent. This model therefore provides an accurate description of the lowest-lying excitation process in both OH and OD molecules.