J/ApJ/519/697 Molecular study of HC_3_NH^+^+e^-^ (Osamura+, 1999) ================================================================================ A molecular orbital study of the HC_3_NH^+^+e^-^ dissociative recombination and its role in the production of cyanoacetylene isomers in interstellar clouds Osamura Y., Fukuzawa K., Terzieva R., Herbst E. =1999ApJ...519..697O ================================================================================ ADC_Keywords: Atomic physics ; Interstellar medium Keywords: ISM: molecules - molecular processes Abstract: The dissociative recombination reaction between HC_3_NH^+^ and electrons is an important process in the chemistry of interstellar clouds. Motivated by the evidence that HCN and its metastable isomer HNC are both formed via the dissociative recombination reaction of HCNH^+^, we have examined the potential energy surface for the dissociation of the transient HC_3_NH following the recombination between HC_3_NH^+^ and electrons. We find that HC_3_NH^+^ gains 151 kcal mol^-1^ energy by the neutralization; this energy is high enough to isomerize HC_3_NH to HCCNCH, as well as to dissociate a hydrogen atom from either end of the molecule. The present calculation suggests, therefore, that the metastable linear and near-linear isomers of HC_3_N, namely, HNC_3_, HCCNC, and HCNCC, can be formed via the dissociative recombination between HC_3_NH^+^ and electrons. Two of these isomers, HNC3 and HCCNC, have already been detected in the dark cloud TMC-1. The unobserved species HCNCC is energetically the least stable. Since interstellar HC_3_N molecules are synthesized predominantly via neutral-neutral reactions, the HC_3_NH^+^ + e^-^ process serves mainly to produce the metastable isomers of HC_3_N. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 59 116 Reactions involving HC_3_N, its isomers, and their protonated ions -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 8 E8.2 cm3/s Const Constant on the rate coefficient (1) 10- 13 F4.1 --- Sp+Index Power law on the rate coefficient equation 15- 59 A45 --- Reaction The Reaction -------------------------------------------------------------------------------- Note (1): Rate coefficients are in the form Const(T/300)^Sp+Index^, where Const is in units of cm^3^.s^-1^, except for the photodissociation of HC_3_N, by internally generated photons, for which Const is unitless and multiplies the cosmic-ray ionization rate {zeta} (s-1). -------------------------------------------------------------------------------- History: From ApJ electronic edition ================================================================================ (End) Greg Schwarz [AAS] 28-Apr-2000