2014MNRAS.437.2351V

A particularly interesting family of molecules that has been identified in the interstellar medium is composed by the cyanopolyynes (HCnN, n = 1, 3, 5, …). Their isomers, the isocyanopolyynes (HCn-1NC), have also been found in such an environment. Because of this, we have chosen to study the mechanism involved in the isomerization reaction of these species with n = 1, 3 and 5, using quantum chemistry methods at temperatures of 298.15, 500, 700, 1000 and 3000K. Our results show that the conversion from isocyanopolyynes to cyanopolyynes is an exothermic process with rate constants several orders of magnitude larger than the reverse reaction at lower temperatures. Rate constants of direct and inverse reactions at lower temperatures are also much faster for n = 1 than those observed for longer chains. In turn, the increase in temperature results in large increments of rate constants while isomerization enthalpy changes remain almost unaltered within the examined temperature range. We also provide parameters for the modified Arrhenius equation as obtained from our best calculations, which can be used to predict rate constants from 298.15 to 3000K. To the best of our knowledge, this is the first kinetic study of such a kind for these isomerization reactions with n = 3 and 5.