Precision spectroscopy and comprehensive analysis of perturbations in the $A{}^1\Pi (v=0$) state of ${}^{13}$C${}^{18}$O

Abstract

We have reinvestigated the A${}^1\Pi$$(v=0)$ level of ${}^{13}$C${}^{18}$O\ using new high-resolution spectra obtained via multi-photon laser excitation as well as with synchrotron-based Fourier-transform absorption spectroscopy of the A${}^1\Pi -{\text{X}}^1{\Sigma }^{+}$$(0,0)$, e${}^3{\Sigma }^{-}-{\text{X}}^1{\Sigma }^{+}$$(1,0)$, d${}^3\Delta -{\text{X}}^1{\Sigma }^{+}$$(4,0)$, a${}^{\prime 3}{\Sigma }^{+}-{\text{X}}^1{\Sigma }^{+}$$(9,0)$, and \atX$(11,0)$ bands. In addition, Fourier-transform emission spectroscopy in the visible range is performed on the ${\mathrm{B}}^1{\Sigma }^{+}-{\mathrm{A}}^1\Pi$$(0,0)$ band. Spectra of the \BX$(0,0)$ band are measured in order to tie information from the latter emission data to the level structure of A${}^1\Pi$$(v=0)$. The high pressures in the absorption cell at the synchrotron and the high temperatures in the emission discharge permitted monitoring of high rotational quantum levels in A${}^1\Pi$$(v=0)$ up to $J=43$. All information, in total over 900 spectral lines, was included in an effective-Hamiltonian analysis of the A${}^1\Pi (v=0,J)$ levels that are directly perturbed by the e${}^3{\Sigma }^{-}$$(v=1)$, d${}^3\Delta$$(v=4)$, a${}^{\prime 3}{\Sigma }^{+}$$(v=9)$, d${}^3\Delta$$(v=0)$, I${}^1{\Sigma }^{-}$$(v=0,1)$ close-lying levels and the e${}^3{\Sigma }^{-}$$(v=0,2)$, d${}^3\Delta$$(v=3,5)$, a${}^{\prime 3}{\Sigma }^{+}$$(v=8,10)$ remote levels, as well being indirectly influenced by the a${}^3\Pi$$(v=10,11)$ state. The influence of nine further perturber levels and their interactions was investigated and are not significant for reproducing the present experimental data. This analysis leads to a much improved description in terms of molecular constants and interaction parameters, compared to previous studies of the same energy region for other CO isotopologues.

arXiv commentaccepted Molecular Physics

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