Variational quantum mechanical and active database approaches to the rotational-vibrational spectroscopy of ketene, H2CCO

Abstract

A variational quantum mechanical protocol is presented for the computation of rovibrational energy levels of semirigid molecules using discrete variable representation of the Eckart-Watson Hamiltonian, a complete, "exact" inclusion of the potential energy surface, and selection of a vibrational subspace. Molecular symmetry is exploited via a symmetry-adapted Lanczos algorithm. Besides symmetry labels, zeroth-order rigid-rotor and harmonic-oscillator quantum numbers are employed to characterize the computed rovibrational states. Using the computational molecular spectroscopy algorithm presented, a large number of rovibrational states, up to J = 50, of the ground electronic state of the parent isotopologue of ketene, H(2) (12)C=(12)C=(16)O, were computed and characterized. Based on 12 references, altogether 3982 measured and assigned rovibrational transitions of H(2) (12)C=(12)C=(16)O have been collected, from which 3194 were validated. These transitions form two spectroscopic networks (SN). The ortho and the para SNs contain 2489 and 705 validated transitions and 1251 and 471 validated energy levels, respectively. The computed energy levels are compared with energy levels obtained, up to J = 41, via an inversion protocol based on this collection of validated measured rovibrational transitions. The accurate inverted energy levels allow new assignments to be proposed. Some regularities and irregularities in the rovibrational spectrum of ketene are elucidated.

A database of water transitions from experiment and theory (IUPAC Technical Report)

“…MARVEL was originally developed for the TG's work on water but can, of course, be adapted for the analysis of high-resolution rovibrational spectra of any other molecule, as well; in fact, it has been used to treat H 2 D + [60], D 2 H + [60], and ketene (CH 2 CO) [61].…”

Simple molecules as complex systems

“…As to SNs, where the number of experimentally measured links is about an order of magnitude larger than the number of nodes252729303132, the question is whether there is a mean value for the number of transitions that an “average” energy level has. To answer this question one needs to investigate the distribution of the links among the nodes.…”

Perspective: Computing (ro-)vibrational spectra of molecules with more than four atoms

“…The basis functions are products of vibrational wavefunctions (which are contracted basis functions) and Wigner functions. 2,65,88,89,91 All SF/D calculations are limited by the size of the Hamiltonian matrix. Using commonly accessible computers it is not possible to use a direct diagonalization algorithm for matrices whose size is larger than 100'000.…”

“…They compute contracted vibrational functions labelled by K. Instead, one can use solutions of the J = 0, K = 0 block as vibrational basis functions. 2, [63][64][65][66] Type 2 contracted functions have important advantages. (1) The matrix-vector products one must evaluate to compute energy levels with an iterative eigensolver are less costly.…”

“…This contraction reduces the size of the basis by a significant factor. 65,66 D. General PES/iterative-eigensolver/pruned-basis (G/I/P) methods SF/D/P and SF/I/P methods use a basis of selected products of univariate functions. In the SF/D/P case, the pruned basis is small enough that it is possible to use a direct eigensolver.…”