Hua-Gen Yu, Steve Ndengue, Jun Li, Richard Dawes, Hua Guo, Vivbrational levels of the simplest Criegee intermediate (CH2OO) from full-dimensional Lanczos, MCTDH and MULTIMODE calculations, J. Chem. Phys. 143, 084311 (2015).

 

Abstract

 Accurate vibrational energy levels of the simplest Criegee intermediate (CH2OO) are determined on a recently developed ab initio based nine-dimensional potential energy surface using three quantum mechanical methods. The first is based a conventional basis expansion with an exact Hamiltonian, which is expected to yield benchmark values. The second and more efficient method is based on the multi-configurational time-dependent Hartree (MCTDH) method in which the potential energy surface is refit to conform with the sums-of-products requirement of MCTDH. Finally, the energy levels were computed with a vibrational self-consistent field/vibrational configuration interaction(VSCF/VCI) method in MULTIMODE. The fundamental frequencies obtained from the MULTIMODE and MCTDH methods are found to be within a few wave numbers of exact values, although some errors exist at overtones and combination levels. In addition, the infra-red spectrum up to 6000 cm-1 was predicted with MULTIMODE wavefunctions and an ab initio based dipole surface.