Simulated Photoelectron Spectra of the Cyanide-Water Anion via Quasiclassical Molecular Dynamics

We present the simulated photoelectron spectrum (PBS) for cyanide-water CN(H2O)(-) based on quasiclassical trajectory molecular dynamics (QCT-MD). Using density functional theory to generate trajectories and to calculate vertical detachment energies, we obtain simulated spectra that are in qualitative agreement with experiment. We obtain a theoretical 12 -> 300 K temperature red shift of 0.1 eV as compared to an experimental redshift of 0.25 eV. The calculated linewidths of 0.3 eV are in excellent agreement with experiment. Our trajectories show that the temperature red shift as being dominated by dynamics within the basin of the N-bound minimum, however, at 300 K we predict conversion into the basin of the C-bound minimum, equilibrating at a 80:20 ratio of N-vs C-bound mixture. We discuss the potential advantages of QCT-MD over anharmonic Franck-Condon analysis such as natural incorporation of anharmonicity (as necessary for weakly bound systems), and reduced computational scaling, but also drawbacks such as neglect of final-state (e.g., Duschinsky) effects.