Quantum chemical calculations for the dissociative recombination of HCN+ and HNC+

A theoretical investigation of the dissociative recombination (DR) of HCN+( X (2)Pi), HNC+(X (2)Sigma) and HCN+(A (2)Sigma) has been undertaken in orde r to complement the recent experimental measurement (Sheehan C, Le Padellec A, Lennard WN, Talbi D and Mitchell J B A 1999 J. Phys. B: At. Mel. Opt. P hys. 32 3347) of the DR of [CHN](+). Using quantum chemical methods, we hav e shown that the dissociative recombination of HNC+(X (2)Sigma) should invo lve the indirect mechanism while that of HCN+(X (2)Pi) and HCN+(A (2)Sigma) should be possible through both direct and indirect processes. Our theoret ical study therefore suggests that HCN+(X (2)Pi) and HCN+(A (2)Sigma) shoul d recombine much more rapidly than HNC+(X (2)Sigma) explaining the large ra te coefficient measured for the DR of HCN+ compared with the HNC+ case.