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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.

The dissociative recombination rate coefficients for H+3, HN+2, and HCO+ are determined at 110, 210, and 273 K by monitoring the decay of the infrared absorption signals as a function of time. The rate coefficients are 1.8, 7.0, and 3.1 in units of 10−7 cm3 s−1 for H+3, HN+2, and HCO+, respectively, at 273 K. These values agree very well with those obtained using the stationary afterglow or the merged beam techniques, but the values for H+3 disagree with that obtained by Smith and co-workers (≤2×10−8 cm3 s−1) using the flowing afterglow/Langmuir probe method. The rate coefficients for H+3 and HCO+ disagree with theory which has predicted very slow dissociative recombinations in the lower vibrational states. The temperature dependences obtained here, although the temperature range is rather limited, are consistent with those obtained previously using the stationary afterglow (for H+3 and HCO+) and the merged beam (for HN+2) techniques. The measurements are extended to several vibration–rotation levels and no significant rotation dependence of the rate coefficients is observed. It has also been found that the ions investigated here can be equally abundant at ice temperature as at liquid nitrogen temperature.

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