The Swan System of C ₂ : A Global Analysis of Fourier Transform Emission Spectra

Abstract

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.

Deperturbation study of the state of C2 by applying degenerate and two-color resonant four-wave mixing

“…A recent study of the d 3 P g À c 3 R þ u system by Joester et al [27] revealed perturbations in the d 3 P g ; v 0 ¼ 4 level. The supersonically cooled radicals exhibiting only low J levels and, therefore, less congestion disclose perturbations that are in significant disagreement with the reported values from Tanabashi et al [20,25].…”

“…The bands are denoted by the standard nomenclature ðv 0 ; v 00 Þ. On the bottom, a simulation of the (4, 3) band is shown inverted that has been computed by the pgopher program developed by Western [35] and using molecular constants from Tanabashi et al [20,25]. As mentioned above, a global analysis of the rotational perturbations has not been performed and is neglected in the simulation.…”

“…Obviously, an unambiguous assignment of these lines is mandatory to disentangle the spectral observations. However, the most recent molecular constants [20] are not sufficiently complete to model all features of the d 3 P g À a 3 P u system because of local perturbations in many vibrational levels. Despite the fact that the d 3 P g À a 3 P u system of C 2 has been studied for over 200 years, a complete rotational analysis has not been achieved.…”

“…Recently, Tanabashi et al [20,25] re-investigated the Swan system in detail by applying high-resolution Fourier transform spectroscopy for vibrational bands with v 0 ¼ 0 À 10 and v 00 ¼ 0 À 9. Many line positions and assignments from earlier work [26], especially for v 0 ¼ 4; 5; 6 had to be corrected.…”

Examining the temporal evolution of hypervelocity impact phenomena via high-speed imaging and ultraviolet-visible emission spectroscopy

“…43 These Swan bands are well known in carbon-rich plasma spectra originating from several sources, including high-speed impacts, the ablation of graphite, the electrical discharge of acetylene, or chemical vapor deposition. 8,10,[47][48][49][50][51] Schultz et al previously examined spectral signatures from oblique impacts into porous particulates and found evidence that Swan band emission can originate from hydrocarbon bearing targets or from the dissociation of carbon-rich compounds under low atmospheric pressure conditions. 10 Additional work by Sugita and Schultz investigated impacts of polycarbonate on water and yielded strong C 2 Swan band emission, which they attributed to a high-temperature carbon-rich vapor that was ablated from rapidly moving, fine-grain fragments in the expanding impact-induced vapor cloud.…”