Perturbation of the a3Π(v = 9) and d3Δ (v = 2) states of CO

One hundred and ninety-nine spectral lines in the (9, 1) overtone band of the a3Π state of the CO molecule in the near infrared region of 12,350-12,850 cm−1 are observed by employing optical heterodyne and magnetic rotation enhanced concentration modulation spectroscopy for the first time due to the strong perturbation between the v = 9 of a3Π and v = 2 of d3Δ levels. Additionally, 680 lines in the (2, 1) band of CO a3Π-d3Δ system are observed. Therefore, the most accurate molecular constants of these two perturbed levels, together with their perturbation constants, are obtained by non-linear least squares fitting using effective Hamiltonians. Our results show the improvement of about one order.