Resonance-enhanced multiphoton ionisation photoelectron spectroscopy of the ClO radical: the C 2Σ− state

Abstract

A (2 + 1) one-colour resonance-enhanced multiphoton ionisation study is carried out on the C ²Σ⁻ state of the ClO radical in the one-photon energy range 29500–31250 cm⁻¹. The ClO radical is produced by one-photon photolysis of ClO₂ employing 359.2 nm photons derived from a separate laser. In this way a significant concentration of vibrationally excited ClO in its spin–orbit split X ²Π_Ω (Ω=3/2 or 1/2) electronic ground state is produced. In addition to mass-resolved excitation spectra, kinetic-energy resolved photoelectron spectra for the X³Σ⁻(⁺)←C ²Σ⁻(′=3–5) transitions are measured. These transitions are not completely Franck–Condon diagonal, and indicate a decrease in bond length on removal of the Rydberg electron from the C ²Σ⁻ state. In addition to an unambiguous assignment of the C ²Σ⁻ state, valuable information is obtained on the degree of vibrational excitation with which the nascent ClO radical is formed in the photolysis of ClO₂ . Analysis of the photoelectron spectra is supported by Franck–Condon calculations based on potential energy curves either from experimental spectroscopic parameters, or obtained by theoretical ab initio methods.