THERMOCHEMISTRY OF HNC, HNC+, AND CF3+

In the course of mechanistic studies on HCN+ isomerization in reaction with CO and CO2, we have fortuitously determined the heats of formati on of HNC and HNC+ with good precision. The uncertainty is the uncerta inty in the heat of formation of HCN, +/- 1 kcal mol(-1). This appears to be the first precise experimental determination of these energies. Several prior theoretical calculations have produced reasonable energ y values. We also observed the reaction of HCN+ with CF4 to be slightl y endothermic, which allows the determination of an upper limit on the threshold energy for CF4 --> CF3+ + F of 14.28 eV, in excellent agree ment with several prior determinations but in sharp disagreement with the most recent determination. (C) 1998 American Institute of Physics.