Photodissociation branching ratios of ¹³C¹⁶O and ¹²C¹⁸O in the vacuum ultraviolet region from 107 800 to 109 700 cm⁻¹

¹ Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China
e-mail: honggao2017@iccas.ac.cn; chengmin@iccas.ac.cn
² University of Chinese Academy of Sciences, Beijing, 100049, PR China

Received: 7 January 2020
Accepted: 21 March 2020

Abstract

In this study, we present C⁺ ion photofragment spectroscopic studies and photodissociation branching ratio measurements for two CO isotopologs, ¹³C¹⁶O and ¹²C¹⁸O, in the vacuum ultraviolet (VUV) region from 107 800 cm⁻¹ (92.76 nm) to 109 700 cm⁻¹ (91.16 nm) using a time-slice velocity-map imaging setup and a tunable VUV laser radiation source generated by the two-photon resonance-enhanced four-wave mixing technique. Several absorption bands of ¹²C¹⁶O in the above energy region are reinvestigated up to higher rotational levels compared with previous studies. The results are compared among ¹²C¹⁶O, ¹³C¹⁶O, and ¹²C¹⁸O on a state-by-state basis, and the photodissociation branching ratios for channels C(¹D) + O(³P), and C(³P) + O(¹D) are dramatically changed for most of the absorption bands due to the substitutions of ¹²C by ¹³C and ¹⁶O by ¹⁸O. The branching ratios of ¹³C¹⁶O and ¹²C¹⁸O are close to each other due to their similar reduced masses. The strong and selective isotope effects obtained here not only provide useful information for understanding the complicated predissociation dynamics of CO, but are also important for developing a comprehensive photochemical model for explaining the C and O isotope heterogeneities as observed in the Solar System.