Theoretical spin–rovibronic 2A1(Πu)–2B1 spectrum of the H2O+, HDO+, and D2O+ cations

Abstract

Based on extensive ab initio multiconfiguration reference configuration interaction (MRCI) electronic structure calculations, three-dimensional potential energy functions for the A 2A1(Πu)–X 2B1 linear/bent Renner–Teller systems of H2O+, HDO+, and D2O+ have been generated and used in beyond Born–Oppenheimer calculations of the spin–rovibronic energy levels by a variational approach. The effects of anharmonicity, rotation–vibration, electronic angular momenta, and spin coupling effects have been accounted for. For H2O+, HDO+, and D2O+ vibronic band origins for the bending levels to Ka=5 and for selected stretching and combination levels are given. Almost all experimentally known data have been reproduced with an accuracy better than 10 cm−1 after minor modifications of the ab initio potential energy functions. Our calculated values will facilitate further experimental assignments. A consistent interpretation of the photoelectron spectra for the different isotopes of water is given. Previous assignments of the bending modes in the A 2A1 state have been revised by two quantum numbers.

Stretch-Bender Calculations of the Rovibronic Energies in the Excited, Ã2A1, Electronic State of NH2 and of the Near-Resonant High-Lying Levels of the X̃2B1 State

“…This is particularly important when the final vibronic wavefunctions are very complicated, owing to the large number of basis states which can be coupled together. This makes node-counting methods difficult to use, as noted in several papers by Carter, Handy, and their collaborators (16,(21)(22)(23). The calculated value of L z provides a useful method of angular momentum tagging, which complements other methods such as the size and sign of the l-type doubling in K = 1 vibronic states, or the size of the value of the effective symmetric rotor B value in a particular vibronic state,B = 1/2(B + C).…”

Vibronic transition moments and line intensities for H2O+

“…This phenomenon is called the Renner, or Renner-Teller, effect [5]. Brommer et al [3] calculated the rovibronic energies ofX 2 B 1 andà 2 A 1 H 2 O þ by means of a model that incorporates the Renner effect. Their work led to a reassignment of the bending levels (0,v lin 2 ,0) in theà 2 A 1 state that are involved in experimentally observed transitions.…”

“…Brommer et al [3] obtained fully dimensional ab initio potential energy surfaces for theX 2 B 1 andà 2 A 1 electronic states of H 2 O þ . These two electronic states correlate with a 2 P u electronic state at linear configurations so that they are degenerate when the molecule is linear (see Fig.…”

“…This simulation requires knowledge of the absolute values for the vibronic transition moments in theà 2 A 1 !X 2 B 1 and X 2 B 1 !X 2 B 1 emission systems of H 2 O þ . Previous theoretical studies of H 2 O þ in theX 2 B 1 andà 2 A 1 electronic states, including the comprehensive study by Brommer et al [3], are mainly focused on the calculation of rovibronic energies. Jungen et al [4] have calculated relative vibronic intensities by representing theà 2 A 1 !X 2 B 1 electronic transition moment by a model function but thus far, no intensities have been computed from ab initio dipole moment functions and transition moments.…”

Dissociation and predissociation in the ns 1B1 and np1A2 series of H2O

“…Extension of the theory to include Renner-Teller coupling is also planned for the future, although much work remains to be done. An accurate RennerTeller treatment for the two lowest states of H 2 O + , on well converged potential surfaces, was performed some years ago [41]. The strong K a dependence of the coupling appears in the composition of the resulting two component wavefunctions, truncated versions of which would provide the vibrational basis for computation of sine and cosine matrices, analogous to those in eqn (6).…”