Perturbation And Rotational-resolved Spectrum Study On The Triplet Band (d～3△-a～3Ⅱ) Of CO

The CO molecule has been found in extraterrestrial sources and in a variety of experiments, indicating that it plays significant roles in chemical reaction processes, plasmas, interstellar matter, biomedicine, environmental science and other fields. That the CO metastable state, a³Î , can be manipulated by either electric or magnetic fields, together with its long lifetime up to several hundred microseconds, makes it one of the most important candidates for molecular cooling. Therefore, its structural study together with those of other triplet states is essential in future applications. However, information on triplet states is less complete than that for singlet states because the triplet states are often studied via the spin-forbidden transitions to the ground state,In the present paper, the metastable state of CO molecular in an ac glow discharge plasma of carbon monoxide with helium as carrier gas. By employing the optical heterodyne and magnetic rotation enhanced concentration modulation spectroscopy (OH-MR-CMS), the Doppler-limited absorption spectrum of CO in the near infrared and visible regions is observed with high signal-to-noise ratios (typically over 100). More than 1200 lines in the triplet band d³Î”- a³Î  of CO are observed, i.e., 680 lines of the (2,1) band, 628 lines of the (3, 1) band, and 158 lines of the (6, 1) band in the region of 12350-12850cm^-1, 13340-13900cm^-1 and 16850-17100cm^-1, respectively. Furthermore, 199 lines of the (9, 1) overtone band and about 30 lines of the (12, 1) overtone band in the a³Î  state are obtained as well for the first time. Diagonalizing the effective Hamiltonian matrices while considering the perturbation, the positions of the ro-vibrational spectra are calculated for the spectral tentatively assigning. A comprehensive perturbation analysis between the v_d = 2 and v_a = 9 levels and between the v_d =6 and v_a = 12 levels is performed with the molecular constants of the v_a = 1 level in the a state fixed to the precise values obtained in the submillimeter-wave region. Therefore, the most precise molecular constants of these two pair perturbed levels are obtained. All the observed spectra are nonlinear least-squares fitted with weighted errors. That the standard errors of the fit are all about half of our experimental uncertainty bodes well for the reliability of our results which show good agreements with the previous within 3σ errors. Additionally, the improved RKR potential curve of the d³Î” of the CO is constructed using the latest precise equilibrium constants.