Multichannel resonances in near-threshold photodissociation spectra of CH+, SiH+ and GeH+

Abstract

Evidence for multichannel character in resonances which appear in near-threshold photodissociation spectra of the isovalent molecules, CH ⁺ , SiH ⁺ and GeH ⁺ is presented. The spectra were obtained through laser-induced excitation from the X ¹ Σ ⁺ state to near-threshold levels of electronic states which correlate with the lowest dissociation limits, ² P _3/2,1/2 (C ⁺ , Si ⁺ , Ge ⁺ )+ ² S(H), by monitoring the production of the atomic fragment ions. Complementary resonance-width calculations have been carried out using a close-coupling approach. In CH ⁺ we report the discovery of a shape resonance with multichannel character; in SiH ⁺ , where excitations to Feshbach resonances dominate the photodissociation spectrum, we present the first results of multichannel calculations; in GeH ⁺ we report observation of the first photodissociation spectrum involving near-threshold dissociated levels.