FOURIER TRANSFORM ABSORPTION SPECTROSCOPY OF C3 IN THE ν3 ANTISYMMETRIC STRETCH MODE REGION

The C$_3$ molecule has been detected in a variety of astrophysical objects thanks to the well-known 4050 AA~(A$^1Pi_u$--X$^1Sigma ^+ _g$) electronic transition as well as the two IR active modes of the electronic ground state: $nu_2$ ($sim$ 63.42 cm$^{-1}$) and $nu_3$ ($sim$ 2040.02 cm$^{-1}$)footnote{L. Gausset, G. Herzberg, A. Lagerqvist, B. Rosen, Astrophysical Journal, 45--81 (1965); T. F. Giesen et al., The Astrophysical Journal, 551, L181--L184 (2001); K. W. Hinkle, J. J. Keady, P. F. Bernath, Science, 241, 1319--1322 (1988)}. Previous laboratory data in the $nu_3$ region, obtained using diode laser spectroscopy and the photolysis of allene to produce C$_3$, permitted measurement of the fundamental (0,0,1)$Sigma$--(0,0,0)$Sigma$ as well as the hot bands: (0,1,1)$Pi$--(0,1,0)$Pi$; (0,2,1)$Sigma$--(0,2,0)$Sigma$; (0,2,1)$Delta$--(0,2,0)$Delta$ and provided insights on the anharmonicity of the (0,$nnu_2$,1) vibrational patternfootnote{K. Kawaguchi et al., J. Chem. Phys., 91, 1953--1957 (1989)}._x000d_ _x000d_ We have recorded the absorption spectrum of C$_3$ in the 1800--2100 cm$^{-1}$ region (at a resolution of 0.003 cm$^{-1}$) using the Bruker IFS 125 Fourier Transform spectrometer at the AILES beamline of Synchrotron SOLEIL. C$_3$ was produced in a DC discharge of methane heavily diluted in helium. The rovibrational temperature of C$_3$ produced in our discharge is noticeably higher than in Ref. [4], which allowed us to extend measurements to higher $J$ values. More interestingly, we assigned new hot bands involving higher quanta of the $nu_2$ bending states: (0,$nnu_2$,1) with $n$ ranging from 0 to 5. Despite the absence of $Q$ branches for these bands, which results in a possible ambiguous $J$-assignment of $P$ and $R$ lines, the large variety of data considered in this work, in addition to our experimental data and including observations of comet spectra, allows confident assignments