Radiative and predissociative lifetimes of the A 2Σ+ state (v′=0,1) of SH and SD: A highly correlated theoretical investigation

Abstract

Doublet and quartet states of the HS radical correlating with H(2S)+S(3P,1D,1S) were investigated by ab initio calculations, at the CASSCF-MRCI/aug-cc-pV5Z level of theory. Molecular parameters and spectroscopic constants obtained for both the ground (X 2Π) and the first excited (A 2Σ+) states represent the best overall theoretical description of this system to date. Transition moments, transition probabilities, and radiative and predissociative lifetimes were also determined for the X 2Π–A 2Σ+ system. The values calculated for the radiative lifetimes of the A state show that previous results were too large. Theoretical predissociative lifetimes, although quite sensitive to the region of crossing of the potential energy curves, reproduce the experimental trends.

Detection of the mercapto radical SH in the solar atmosphere

“…Our fitting procedure resulted in a value of f 00 = 2.2 × 10 −3 . An even larger value of f 00 was very recently predicted by Resende & Ornellas (2001) who carried out ab initio calculations of SH radiative lifetimes. With the best overall theoretical description of the A 2 Σ − X 2 Π system, they determined the Einstein coefficient for the (0, 0) band as large as 1.818 × 10 6 s −1 , which results in f 00 = 2.896 × 10 −3 .…”

Theoretical investigations of the SH+ and LiS+ cations

“…Indeed, large computations have been performed on the SH lowest electronic states and both theoretical and experimental studies have treated the predissociative nature of the SH(A 2 R + ) state, where, short-range interactions (such as spin-orbit and vibronic) and long-range quantum mechanical interference effects and asymptotic interactions between the repulsive states, are found to play a role during the direct dissociation and the predissociation of this radical [3][4][5][6]. For SH + , the rovibrational constants and the hyperfine structure of its electronic ground state X 3 R À have been obtained using emission [7] and absorption [8] techniques, laser-ion beam spectroscopy [9], laser magnetic resonance [10], ion-selective technique of velocity modulation diode laser spectroscopy [11], submillimeter velocity modulation spectroscopy [12] and Faraday rotation magnetic resonance method [13].…”

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

“…Several ab initio calculations of the SH ground and excited states have been made (Bruna & Hirsch 1987;Resende & Ornellas 2001;Lee et al 2001), and there is one absolute absorption measurement, providing the oscillator strength of the predissociative X 2 Π(v = 0) to A 2 Σ + (v = 0) transition. This measurement was combined with calculated Franck-Condon factors for transition to higher-v A 2 Σ + levels (Resende & Ornellas 2001) and experimental spectroscopic constants (Johns & Ramsay 1961) to estimate the cross section of A − X transitions (neglecting their rotational structure).…”

“…This measurement was combined with calculated Franck-Condon factors for transition to higher-v A 2 Σ + levels (Resende & Ornellas 2001) and experimental spectroscopic constants (Johns & Ramsay 1961) to estimate the cross section of A − X transitions (neglecting their rotational structure). Furthermore, a "reflection" cross section to simulate continuum absorption into the lowest-energy repulsive 2 Σ − state was added, using the potential-energy curves and electronic transition moment of Lee et al (2001), and the methods described in Sect.…”