Energy dependence of the isomerization of HCN+ to HNC+ via ion molecule reactions

The mechanism for isomerization of HCN+ ions to the more stable HNC+ in collision with CO2 at thermal energy has been confirmed to be a double proton transfer in the collision complex. First a proton is transferred from C in HCN+, then, following CN rotation in the complex, the proton is transferred to the N atom, both proton transfers being exothermic. The mechanism has been established by measuring the reaction of HCN+ with CO2 as a function of energy from thermal up to 0.7 eV relative kinetic energy in a selected ion flow drift tube. The isomers are distinguished by the use of monitors that react differently with the two isomers. A similar HCN+ to HNC+ isomerization occurs in thermal collisions with CO.