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

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 H-2(+)(X,nu(+)=0-17, N+=1)+Ar at the center-of-mass collision energies of 1.1 and 2.4 eV. The nu(+)=17 state is the second to the last vibrational level of H-2(+)(X), which lies a mere 0.03 eV below the H-2(+)(X) dissociation limit. The absolute cross sections observed for the formation of Ar+ and ArH+ [sigma(v+)(Ar++ArH+)] from H-2(+)(X,nu(+)=0-4, N+=1) are consistent with previous experiments, exhibiting strong enhancement of the reaction cross section for nu(+)=2. However, the sigma(v+)(Ar++ArH+) values for H-2(+)(X,nu(+)=5-14, N+=1)+Ar are found to be nearly constant. The drop in sigma(v+)(Ar++ArH+) observed for H-2(+)(X,nu(+)=15-17, N+=1)+Ar is attributed to the further dissociation of product ArH+. (C) 2003 American Institute of Physics.