High-resolution one-photon absorption spectroscopy of the $D\,{}^2\Sigma^- \leftarrow X\,{}^2\Pi$ system of radical OH and OD

TL;DR

This study provides high-resolution VUV absorption spectra of OH and OD radicals, quantifies transition parameters, measures excited state lifetimes, and identifies perturbations, advancing understanding of their electronic structure.

Contribution

It presents the first lifetime measurements of the $D$ state levels and details high-resolution spectral data for OH and OD radicals.

Findings

Measured transition frequencies and $f$-values with high precision.

First-time measurement of lifetime broadening of $D$ state levels.

Identified a local perturbation in the $D$ state of OH.

Abstract

Vacuum-ultraviolet (VUV) photoabsorption spectra were recorded of the $A\,{}^2\Sigma^+(v'=0)\leftarrow{}X\,{}^2\Pi(v''=0)$, $D\,{}^2\Sigma^-(v'=0)\leftarrow{}X\,{}^2\Pi(v''=0)$ and $D\,{}^2\Sigma^-(v'=1)\leftarrow{}X\,{}^2\Pi(v''=0)$ bands of the OH and OD radicals generated in a plasma-discharge source using synchrotron radiation as a background continuum coupled with the VUV Fourier-transform spectrometer on the DESIRS beamline of synchrotron SOLEIL. High-resolution spectra permitted the quantification of transition frequencies, relative $f$-values, and natural line broadening. The $f$-values were absolutely calibrated with respect to a previous measurement of $A\,{}^2\Sigma^+(v'=0)\leftarrow{}X\,{}^2\Pi(v''=0)$ ([wang1979]). Lifetime broadening of the excited $D\,{}^2\Sigma^-(v=0)$ and $D\,{}^2\Sigma^-(v=1)$ levels is measured for the first time and compared with previous experimental limits, and implies a lifetime 5 times shorter than a theoretical prediction ([van_der_loo2005]). A local perturbation of the $D\,{}^2\Sigma^-(v=0)$ level in OH was found.