| CO is a simple but important molecule. It plays an important role in many fields, such as plasma physics, combustion science and astrophysics. The a3Πstate with a long radiative lifetime, is the lowest triplet metastable state and lies 6eV above the electronic ground state. It has been extensively analyzed by studying the spin forbidden transition of a3Π-X1∑+ in 1972. The triplet state d3Δhas short radiative lifetime and it is also studied via the spin forbidden transition ofd3Δ-X1∑+. The spectra of the d3Δ-a3Πsystem are difficult both to observe and analyze. It wasn't studied until 1993 by Momona et al.In this thesis, the absorption spectra in the region of 13200-13400 cm-1 and 16850-17200 cm-1 in the d3Δ-a3Πsystem of CO are observed by employing optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy (OH-MR-CMS). The observed spectra are assigned to the (1,0), (4,2) and (6,1) band in the d3Δ-a3Πsystem. It is assisted by A-splitting, the phase characteristic of magnetic rotation spectroscopy, line shape and the intensity distribution. There hundred and sixty two lines are assigned to the (1,0) band and 122 lines to the (4,2) band. Additionally, the perturbation (6,1) band is basically analyzed. The direct measurements of the (1,0) and (4,2) bands were not reported before.The assigned spectral lines are fitted using the non-linear least-squares fitting method. The constants of d3Δstate are floated the fitting while those of the a3Πstate are fixed at those of Wada et al. [J. Mol. Spectrosc.200,196 (2000)]. The final standard deviation is 0.0049 cm-1, less than the experimental uncertainty of 0.007 cm-1. More molecular constants are obtained for the v= 1 level in the d3Δstate, and they are more precise.
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