15min:

D. ZHAO, M. A. HADDAD, Institute for Lasers, Life and Biophotonics Amsterdam, De Boelelaan-1081, NL 1081 HV Amsterdam, Netherlands; H. LINNARTZ, Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, and Institute for Lasers, Life and Biophotonics Amsterdam, De Boelelaan 1081, NL-1081 HV Amsterdam, Netherlands; W. UBACHS, Institute for Lasers, Life and Biophotonics Amsterdam, De Boelelaan-1081, NL 1081 HV Amsterdam, Netherlands.

The linear carbon chain radicals have been topic of a series of spectroscopic studies. The hexatriynyl radical C₆H (and deuterated equivalent C₆D), a member of the linear C_nH series, has attracted renewed interest in recent years after the astronomical identification of its chemically related anion C₆H^- and its low-lying 11₁ µ² vobronic state.

In this talk, rotationally resolved spectra of the B² - X² 0₀⁰ and 11₁¹ transitions of both C₆H and C₆D are presented. Cavity ringdown spectroscopy is used to record the spectra in direct absorption through a supersonically expanding planar plasma. The µ² - µ² 11₁¹ vobronic hot bands are observed for the first time. Heavy rotational perturbations are found in the upper levels of C₆D. Precise spectroscopic parameters for the 11¹ µ² levels of both C₆H and C₆D are determined for the first time, and the spectroscopic parameters for the B² 0⁰ states are also improved. The Renner-Teller interaction is also discussed to estimate the excitation energies of the low-lying 11₁ µ² vibronic states.