München 2004 – scientific programme

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MO: Molekülphysik

MO 3: Elektronische Überg
änge

MO 3.8: Talk

Monday, March 22, 2004, 12:45–13:00, HS 355

Spectroscopy of the XeC₂ molecule in Xenon, Argon and Krypton matrices — •Marcin Frankowski, Alice M. Smith-Gicklhorn, and Vladimir E. Bondybey — Institut für Physikalische und Theoretische Chemie, Technische Universität München, Lichtenbergstr. 4, 85748, Garching, Germany

A self-igniting DC-electric discharge of C₂H₂ in Xe (matrix gas) or C₂H₂/Xe in Ar or Kr (matrix gases) is used to produce and study the XeC₂ molecule in these various rare gases at 12 K. Unlike in Ar and Kr matrices, the well-known electronic spectra of C₂ is completely absent in a Xe matrix. This together with annealing experiments in Ar matrices indicate that ground state Xe and C₂ react uniquely and without a barrier to form the XeC₂ molecule. The infrared-active C-C stretch of this compound is found to be close to the C-C stretching frequency of C₂⁻ anion, in excellent agreement with our density functional theoretical (DFT) calculations which yield a XeCC singlet species bent by 148.6^o and with substantial charge separation approaching Xe⁺C₂⁻ and a notably short, 2.107 Å, Xe-C bond. The spectra of the Xe-¹³C-¹²C, Xe-¹²C-¹³C and Xe-¹³C-¹³C species are also obtained and the isotopic shifts are in excellent agreement with the DFT predictions, although not sufficient to distinguish a bent from a linear structure.

Numerous broad absorptions centered near 423 nm (in Xe) are observed which are clearly due to the XeC₂ molecule. Laser-induced fluorescence studies reveal a near-infrared emission likely due to XeC₂ but not yet understood.