Theoretical Studies On Molecular Vibrational Excited States And Photodissociation Dynamics Using Quantum Recursive Methods

Quantum recursive methods have been one of the major trends in studying molecular spectroscopy and dynamics in current theoretical chemical research. In this work, we used two Krylov subspace based methods (Lanczos and Chebyshev) to study the spectroscopy and dynamics of HCN and HCCH molecules.For HCN molecule, we obtained the potential energy surfaces and transition dipole moments for its two lowest excited electronic singlet states using high-level ab initio calculations. Based on these information, we studied the resonance spectra and predissociation dynamics on these two states. For the first absorption band, the CN radical is found to be predominantly in its ground vibrational state, while the rotational distribution is of highly oscillatory structure. On the other hand, the absorption spectrum of DCN has a feature of clustering of resonance states. We also found that Fermi resonance plays an important role in the predissociation dynamics for the first two absorption bands. Accordingly, the beta band is reassigned to its 11An state.Using a modified SLP method, we calculated the resonance emission spectra of acetylene from several vibrational states of the excited A state. The calculation is performed with a full dimensional quantum method, and the converged vibrational levels are obtained and assigned up to 13000 cm-1. In addition, using some artificial spectra, we identified that the normal-to-local mode transition in bending mode will occur around 7000 ~ 10000 cm-1, in excellent agreement with the experimental observations.