Vibrational energy levels of hydrogen cyanide.

Sixty-nine vibrational energy levels have been calculated for HCN, using an ab initio potential energy function adjusted to the fundamentals, and also an empirical potential function by Murrell et al. The energy levels were calculated variationally, using a novel direct CI procedure analogous to methods widely used in electronic structure theory. The present paper includes states with up to four quanta of excitation distributed among the four modes. Agreement with experimental spectra is good. [ABSTRACT FROM AUTHOR]