The C 2 Swan system (d 3 Å g -a 3 Å u ) was observed in emission for the Áv ¼ À3 to Áv ¼ þ2 sequences in the 14,000Y 24,000 cm À1 spectral range using a Fourier transform spectrometer. We carried out a global simultaneous fit by including a wide range of vibrational states. A total of 34 bands with v 0 ¼ 0Y10 and v 00 ¼ 0Y9 were rotationally assigned. Numerous discrepancies were found in the assignments and in the measured transition wavenumbers between the new measurements and previous results. Most of the measured transition wavenumbers and their assignments for relatively low-v bands agreed with published data. On the contrary, for high-v bands our line positions and assignments disagreed with the tabulated literature values. In particular, the lines of six bands involving the levels with v 0 ¼ 4, 5, and 6 are almost completely different from the previous work. Major sources of the disagreement are thought to be line congestion and perturbations found in these bands. From the analysis, perturbations for v 0 ¼ 0, 1, 2, 4, 6, 8, 9, and 10 in the d 3 Å g state were identified. A study of these rotational perturbations suggest that some of them are likely caused by interactions with high-v levels of the b 3 AE À g state.

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