Highly vibrationally excited HCN/HNC: Eigenvalues, wave functions, and stimulated emission pumping spectra

We report the large scale calculation of accurate vibrational eigenstates of X̃ state HCN/HNC up to ∼37 000 cm−1. The discrete variable representation-distributed Gaussian basis (DVR-DGB) approach is used. In the final major computational step, large dense Hamiltonian matrices (≥11 000 rows or columns) must be diagonalized. The use of new software for out-of-core eigenproblems is described in some detail. Representative wave functions of high lying vibrational eigenstates near the isomerization barrier and at energies up to 39 313 cm−1 are presented. Theoretical stimulated emission pumping (SEP) spectra for several initial (Ã) vibrational states are presented along with calculations of the quantum survival probability for these spectra. The spectra range from being dominated by localized eigenstates to being dominated by delocalized eigenstates, depending on the geometry of each initial state. In addition, time-dependent expectation values of the coordinates of the evolving wave packet are plotted.