Nascent rovibrational distributions of HCl+(A 2∑+) and HBr+(A 2∑+) produced from He(2 3S) Penning ionization of HCl and HBr

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Abstract
He(2 3S) Penning ionization of HCl and HBr leading to HCl+(A) and HBr+(A) has been investigated spectroscopically by using a low-pressure experimental apparatus coupled with a flowing afterglow source. The vibrational distribution of HCl+(A) agrees well with the result obtained by Penning ionization electron spectroscopy (PIES), which shows a Franck–Condon like distribution. In contrast, the vibrational distribution of HBr+(A) is more deexcited than the PIES one shifting to lower vibrational levels relative to Franck–Condon factors for ionization. These findings indicate that the collisional perturbation occurs only at the entrance channel for the He(2 3S)/HCl system, while at both entrance and exit ones for the He(2 3S)/HBr system. The rotational temperature of HCl+(A) decreases from 600±100 K for v′=0 to 300±100 K for v′=5, while that of HBr+(A) is 450±50 K for v′=0 and 400±50 K for v′=1.