Rotationally resolved spectroscopy of the Ã A21←X̃ B21 transition of H2S+ above the barrier to linearity using the mass-analyzed threshold ionization photofragment excitation technique

Abstract

The A (2)A(1)<--X (2)B(1) transitions of H(2)S(+) above the barrier to linearity have been investigated with the energy resolution high enough to identify individual rotational transition lines for the first time. The rotational cooling of the cation is achieved either by the direct ionization or mass-analyzed threshold ionization (MATI) technique employed in the vacuum-ultraviolet laser excitation of the jet-cooled H(2)S. Subsequent photoexcitation leads to the H(2)S(+)-->H(2)+S(+) dissociation and the S(+) product yield taken as a function of the excitation energy gives the photofragment excitation (PHOFEX) spectra. The combined use of MATI and PHOFEX techniques greatly simplifies the spectrum allowing the accurate identification of the rotationally resolved bands which is otherwise a formidable task due to the intrinsic complexity of the A (2)A(1)<--X (2)B(1) transition. Highly excited states of A(0,7,0), A(0,8,0), and A(0,9,0) vibronic levels with different K quantum numbers which are located above the barrier to linearity are thoroughly investigated. The bent-to-quasilinear transition of H(2)S(+) above the barrier to linearity shows the characteristics of the Renner-Teller effect, showing the large A rotational constant and strong intensity borrowing of the highly vibrationally excited ground levels such as X(0,23,0) or X(0,24,0) in the dipole-allowed excitation. Spectroscopic parameters of term values, rotational, and spin-orbit coupling constants are precisely determined in this work, providing the most quantitative spectroscopic structure of the H(2)S(+) to date. Quantum-state dependent photodissociation dynamics are also discussed from spectral features of PHOFEX.

The Renner–Teller effect observed in the and electronic states of H2S+

“…This is shown in Table 6, where it can be seen that, below the wavenumber limit of the emission spectrum of H 2 S + , there is good agreement between the spectrum of H 2 S + [3,5] and that of the MATI-PHOFEX spectrum of Han et al [10]. Where we are unable to make a direct comparison with the higher lying levels of the MATI-PHOFEX spectrum, in Table 6, we can see that there is an almost constant energy shift between the levels of the emission spectrum of theà 2 A 1 state of H 2 S + [3,5] and the higher lying levels of the MATI-PHOFEX spectrum [10]. Downloaded by [New York University] at 04:31 30 May 2015 Table 6.…”

“…In order to compare the rotationally resolved spectra of Han et al [10] with the emission spectra of H 2 S + and D 2 S + , we have to take into account the limitations of the emission spectra [3,5]. The spectrum of theà 2 A 1 state of H 2 S + with K a ≥ 1 is cut-off above v 2 = 6, and the remainder with K a = 0 disappears completely above v 2 = 7.…”

“…Han et al [10] have concentrated on the MATI-PHOFEX spectra of H 2 S + , we have chosen to compare their spectra with those of the emission spectrum of theà 2 A 1 state of H 2 S + . This is shown in Table 6, where it can be seen that, below the wavenumber limit of the emission spectrum of H 2 S + , there is good agreement between the spectrum of H 2 S + [3,5] and that of the MATI-PHOFEX spectrum of Han et al [10].…”

“…Downloaded by [New York University] at 04:31 30 May 2015 Table 6. A comparison between the emission spectra of H 2 S + of DHR [3], DJR [5] and the MATI-PHOFEX spectra of Han, Kang and Kim (HKK) [10] in the spectral region between 23,400 and 26,000 cm −1 . The emission spectrum recorded by DJR is completely predissociated above 24,950 cm −1 .…”

“…Entries are F 1 − F 1 followed by F 2 − F 2 . [3]; DJR [5]; HKK [10]. P -perturbed, * -overlapped, diff.…”