Ab initio investigation of the vibronic spectrum involving the two lowest-lying electronic states of HCCO

Abstract

The results of ab initio calculations of the vibronic spectra involving both lowest-lying states X2A″ and A2A′ of the ketenyl radical HCCO are presented. Potential energy surfaces are computed by means of the coupled cluster method with perturbative triple corrections [CCSD(T)]. A recently developed ab initio approach for the treatment of the Renner–Teller effect in tetra-atomic asymmetric molecules is applied to calculate the vibronic energy levels.

Perturbative Handling of the Renner–Teller Effect and Spin–Orbit Coupling in Π Electronic States of Triatomic and Tetra-atomic Molecules

“…where µ T = 2m M R 2 r 2 M R 2 + m(R + 2r ) 2 , µ C = 2m Mr 2 M + m [28] are the reduced masses for the trans and cis bending vibrations,…”

“…Such an approach to the RennerTeller effect in tetra-atomic molecules has been developed in our laboratory (18,19,22,23). The range of its applicability has continuously been extended so that it enables us now to tackle also the spin-orbit and magnetic hyperfine effects (24)(25)(26), as well as large-amplitude bending vibrations (27,28). It has been employed to calculate vibronic spectra of several species in and electronic states, e.g., C 2 H + 2 (23,24), (25,26,29), HCCO (28), and HCCS (30).…”

“…The range of its applicability has continuously been extended so that it enables us now to tackle also the spin-orbit and magnetic hyperfine effects (24)(25)(26), as well as large-amplitude bending vibrations (27,28). It has been employed to calculate vibronic spectra of several species in and electronic states, e.g., C 2 H + 2 (23,24), (25,26,29), HCCO (28), and HCCS (30). However, the availability of such program packages for ab initio handling of the problem considered does not call into question the usefulness of perturbative approaches for interpretation of a usually very restricted sample of experimental findings.…”

An ab initio model for handling the Renner–Teller effect in tetra-atomic molecules. I. Introduction of coordinates and the Hamiltonian

“…Treatment of large-amplitude bending vibrations proposed in Ref. [35] will be improved [49]. Finally, we shall discuss in some detail the RT effect in D and for the first time in U electronic states of tetra-atomic molecules.…”

“…The main practical advantage of this method was that it made possible to obtain the term values and the wave functions for all (bending) vibronic levels of interest. It enables also handling the interplay between the vibronic, spin-orbit [29,17], magnetic hyperfine couplings [30,31,[44][45][46][47], and the effects of large-amplitude bending vibrations [32][33][34][35]. Perturbative formulae were derived for a number of cases not handled by PK (particularly those involving the spinorbit coupling) [17,32,34,37,40,41,43].…”