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Title:Study of infrared emission spectroscopy for the B1∆G-A1ΠU AND B′1ΣG+-A1ΠU systems of c2
Author(s):Tang, Jian
Contributor(s):Bernath, Peter F.; Kawaguchi, Kentarou; Chen, Wang
Abstract:Recently, we carried out the perturbation analysis of C$_2$ spectra and identified forbidden singlet-triplet intersystem transitions, which aroused further interest in other C$_2$ spectra for the many low-lying electronic states of this fundamental molecule. In 1988, the $B^{1}\Delta_{g}$-$A^{1}\Pi_{u}$ and $B'^{1}\Sigma_{g}^{+}$-$A^{1}\Pi_{u}$ band systems were discovered by Douay et al.,\footnote{M. Douay, R. Nietmann and P. F. Bernath, \it{J. Mol. Spectrosc.}, \bf{131}, \rm 261 (1988).} who observed eight bands of the $B^{1}\Delta_{g}$-$A^{1}\Pi_{u}$ system with v up to 5 for the $B^{1}\Delta_{g}$ state and six bands of the $B'^{1}\Sigma_{g}^{+}$-$A^{1}\Pi_{u}$ system with v up to 3 for the $B'^{1}\Sigma_{g}^{+}$ state in the Fourier transform infrared emission spectra of hydrocarbon discharges. In the work presented here, we identified twenty-four bands of the two systems, among which the $B'^{1}\Sigma_{g}^{+}$ v = 4 and the $B^{1}\Delta_{g}$ v = 6, 7 and 8 vibrational levels involved in nine bands were studied for the first time. A direct global analysis with Dunham parameters was carried out satisfactorily for the $B^{1}\Delta_{g}$-$A^{1}\Pi_{u}$ system except for a small perturbation in the $B^{1}\Delta_{g}$ v = 6 level. The calculated rovibrational term energies up to $B^{1}\Delta_{g}$ v = 12 showed that the level crossing between the $B^{1}\Delta_{g}$ and $d^{3}\Pi_{g}$ states is responsible for many of the prominent perturbations in the Swan system observed previously.\footnote{A. Tanabashi, T. Hirao, T. Amano and P. F. Bernath, \it{Astrophys. J. Suppl. Ser.}, \bf{169}, \rm 472 (2007).} Nineteen lines of the $B^{1}\Delta_{g}$-$a^{3}\Pi_{u}$ forbidden transitions were identified and the off-diagonal spin-orbit interaction constant $A_{dB}$ between $d^{3}\Pi_{g}$ and $B^{1}\Delta_{g}$ was derived as 8.3(1) \wn. For the $B'^{1}\Sigma_{g}^{+}$-$A^{1}\Pi_{u}$ system, only individual band analyses for each vibrational level in the $B'^{1}\Sigma_{g}^{+}$ state could be done satisfactorily and Dunham parameters obtained from these effective parameters showed that the anharmonic vibrational constant $\omega_e x_e$ is anomalously small (nearly zero). Inspection of the RKR potential curves for the $B'^{1}\Sigma_{g}^{+}$ and $X^{1}\Sigma_{g}^{+}$ states revealed that an avoided crossing may occur around 30000 \wn, which is responsible for the anomalous molecular constants in these two states.\footnote{W. Chen, K. Kawaguchi, P. F. Bernath, and J. Tang, \it{J. Chem. Phys.}, \bf{144}, \rm 064301 (2016).}
Issue Date:2016-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper/Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2016-08-22

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