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 Title: 2C-R4WM SPECTROSCOPY OF JET COOLED NO3 (II) Author(s): Fukushima, Masaru Contributor(s): Ishiwata, Takashi Subject(s): Radicals Abstract: We have generated NO$_3$ in a supersonic free jet expansion, and observed laser induced fluorescence (~LIF~) and two-color resonant four-wave mixing (~2C-R4WM~) signals. We have measured dispersed fluorescence (~DF~) spectra from single vibronic levels. Among the vibrational levels observed in the DF spectrum from the vibration-less level, the $\nu_1$ and $\nu_3$ fundamental regions (~$\sim$1050 and $\sim$1500 cm$^{-1}$ regions, respectively~) are now active for discussion, and thus we have tried to measure the rotationally resolved 2C-R4WM spectra\footnote{M.~Fukushima and T.~Ishiwata, 71st ISMS, paper RF01 (2016).}. The 2C-R4WM spectrum of the $\nu_3$ fundamental region is consistent with a previous infra-red investigation\footnote{K.~Kawaguchi, et~al., J. Mol. Spectrosco. 268, 85 (2011).}, and that of $\nu_1$ leads to the identification of the $K$ = 0 and $N$ = 1 level of the $\nu_1$ fundamental for the first time. We have found an additional level near $\nu_1$\footnote{M.~Fukushima and T.~Ishiwata, 68th ISMS, paper WJ03 (2013).}, and the 2C-R4WM spectrum of the level shows two rotational transitions separated by 0.27 cm$^{-1}$. Although the 0.27 cm$^{-1}$ separation is about 10 times larger than the spin splitting, $\sim$0.025 cm$^{-1}$, of the $K$ = 0 and $N$ = 1 levels at the other $a_1’$ levels with $l$ = 0, such as vibration-less and $\nu_1$ (~the latter value of which, 0.025 cm$^{-1}$, cannot be resolved under our instrumental resolution~), the two transitions are thought to correspond to those terminating to spin sub-levels, $J$ = 0.5 and = 1.5, at the present. We have assigned the additional level to $3\nu_4$ ($a_1'$) with $l = \pm3$. For $\Sigma$ vibronic levels with $K$ = 0, such as $v_d$ = 1 and $l$ = 1, of a $^2\Pi$ electronic state, it is well known that $^2\Sigma^{(+)}$ and $^2\Sigma^{(-)}$ vibronic levels have relatively large $\Omega$- or $\rho$-type doubling due to non-zero $\Lambda$, in spite of the $\Sigma$ vibronic levels\footnote{J.~Hougen, J.~Chem.~Phys. 36, 519 (1964)}. It is thought that the unexpectedly large spin splitting, 0.27 cm$^{-1}$, is induced by spin-vibration interaction, which has been discussed for degenerate vibronic levels of non-degenerate electronic states, $^2\Sigma$ and $^3\Sigma$, of linear polyatomic molecules\footnote{A.~J.~Merer and J.~M.~Allegretti, Can.~J.~Phys. 49, 2859 (1971).}. Issue Date: 06/20/18 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/100741 DOI: 10.15278/isms.2018.WD02 Other Identifier(s): WD02 Date Available in IDEALS: 2018-08-172018-12-12
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