THE \lq4050~Å ~GROUP\rq OF THE Ã1 Piu - X1 Sigmag+ TRANSITION SYSTEM OF C3.

D. ZHAO, H. LINNARTZ, Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, NL-2300 RA Leiden, the Netherlands; M. A. HADDAD, W. UBACHS, LaserLaB, VU University Amsterdam, De Boelelaan 1081, NL-1081 HV, Amsterdam, The Netherlands; M. R. SCHMIDT, Department of Astrophysics, N. Copernicus Astronomical Center, ul. Rabiańska 8, 87-100 Toruń, Poland; J. KRELOWSKI, Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87-100 Toruń, Poland; G. A. GALAZUTDINOV, Instituto de Astronomia, Universidad Catolica del Norte, Av. Angamos 0610, Antofagasta, Chile.

The \lq4050~Å ~group\rq of C3, which consists of a series of bands of the Ã1 Piu - X1 Sigmag+ electronic transition system, has been of much interest to astronomers as it serves as a remote diagnostic of the physical-chemical conditions in translucent interstellar clouds. In this contribution, we present:

a) The high resolution (R=80~000) detection of eight vibronic bands of C3 in the diffuse translucent cloud towards HD~169454. Four of these vibronic bands are also detected in two additional objects: HD~73882 and HD~154368. Column densities and excitation conditions of C3 are inferred.

b) A laboratory re-examination of the eight vibronic bands observed towards HD~169454 using cavity ring-down spectroscopy and a supersonic plasma jet. High-quality laboratory data build the list of lines with a wavelength accuracy of \textless0.01Å. This is sufficient for the analysis of the observational data. Improved spectroscopic parameters of the corresponding vibronic states are presented. An improved perturbation analysis in the Ã1 Piu (000) state is given as well.

c) The systematic laboratory investigation on the Ã1 Piu - X1 Sigmag+ 000-000 electronic origin band of 13C-substituted C3. Rotationally resolved spectra of all five 13C-isotopologues are recorded in a supersonic plasma expansion by discharging 13C2H2 or 12C2H2/13C2H2 mixtures diluted in noble gas. The Ã1 Piu state molecular constants for all five isotopologues and ground-state molecular constants for 13C12C13C and 12C13C13C are experimentally determined for the first time. This work extends the recent mid-infrared work on the 13C-isotopologues of C3 by Giesen et al.