Predissociation of the c3Πu state of H2, populated after charge exchange of H2+ with several targets at keV energies

Abstract

Abstract A detailed study of the predissocitation of the c 3 Π u state of H 2 has been made with a new, very sensitive, experimental technique. A resolution better than 1% is obtained in the measurement of the released kinetic energy of HH pairs after charge exchange of H 2 + with Ar, H 2 , Mg, Na and Cs by detecting both fragments with a time- and position-sensitive microchannel-plate detector. Eighteen vibrational levels of the c 3 Π u state can be clearly distinguished in the range of 7.2–10.2 eV. Detailed information is extracted from the spectra with the aid of a convolution procedure. The vibrational energy levels of the c 3 Π u state as calculated by Kolos and Rychlewski are found to be correct within the experimental accuracy of 5 meV. Predissociative lifetimes are measured, yielding 6.2±0.5 ns for the lowest rovibrational level (υ = 0, N = 1), which are in good agreement with theoretical calculations of Comtet and de Bruijn. The cross section for charge exchange is observed to increase gradually with the vibrational level and seems to follow the geometrical cross section of the molecule. Rotational excitation during the charge exchange is also found to increase considerably with the vibrational quantum number. The final rotational temperature further depends strongly on the target gas used and increases with the resonance energy defect Δ I in the charge exchange collision.