POTENTIAL-ENERGY SURFACES FOR THE ELECTRONIC DISSOCIATIVE RECOMBINATION OF HCNH- ASTROPHYSICAL IMPLICATIONS ON THE HCN( )HNC ABUNDANCE RATIO/

The two-dimensional potential energy surfaces for the electronic disso ciative recombination reaction HCN+ + e(-) --> HCNH --> HCN + H/HNC H have been computed using large-scale CI calculations. The lowest di ssociative states of (2) Sigma(+) symmetry, resulting in the N-H or C- H bound scission yielding HCN or HNC, respectively are shown to cross the ionic HCNH+ state at its minimum geometry, indicating that the dir ect mechanism of electronic dissociative recombination of HCNH+ is an efficient process which should lead to an equal formation of HCN and H NC. The same conclusion can be drawn for the indirect mechanism: the c rossing between the dissociative states and the lowest Rydberg state o f (2) Sigma symmetry occurs at the same energy for both NH and CH diss ociations. The present calculations support the astophysical hypothesi s of an equal formation of HCN and HNC in the HCNH+ + e(-) dissociativ e recombination process. (C) 1998 Elsevier Science B.V. All rights res erved.