Rovibrational state-selected study of H2+ (X,ν+=0–17, N+=1)+Ar using the pulsed field ionization-photoelectron-secondary ion coincidence scheme

Abstract

A high-resolution pulsed field ionization photoelectron-secondary ion coincidence (PFI-PESICO) method has been developed for absolute cross section measurements of state-selected ion–molecule reactions. Employing this new PFI-PESICO scheme, we have measured rovibrational-state-selected absolute cross sections for the reaction of H2+(X,ν+=0–17, N+=1)+Ar at the center-of-mass collision energies of 1.1 and 2.4 eV. The ν+=17 state is the second to the last vibrational level of H2+(X), which lies a mere 0.03 eV below the H2+(X) dissociation limit. The absolute cross sections observed for the formation of Ar+ and ArH+ [σv+(Ar++ArH+)] from H2+(X,ν+=0–4, N+=1) are consistent with previous experiments, exhibiting strong enhancement of the reaction cross section for ν+=2. However, the σv+(Ar++ArH+) values for H2+(X,ν+=5–14, N+=1)+Ar are found to be nearly constant. The drop in σv+(Ar++ArH+) observed for H2+(X,ν+=15–17, N+=1)+Ar is attributed to the further dissociation of product ArH+.