Spectroscopy of the XeC₂ molecule in xenon, argon, and krypton matrices

Abstract

A self-igniting DC-electric discharge of C 2 H 2 in Xe (matrix gas) or C 2 H 2 and Xe in Ar or Kr (matrix gas) is used to produce and study the XeC 2 molecule in these various rare gases at 12 K. Unlike in Ar and Kr, the wellknown electronic spectra of C 2 is completely absent in a Xe matrix. This together with annealing experiments in Ar matrices indicate that ground state Xe and C 2 react uniquely and without a barrier to form the XeC 2 molecule. The IRactive C-C stretch of this compound is found to be close to the C-C stretching frequency of the C 2 anion, in excellent agreement with our density functional theoretical (DFT) calculations, which yield a XeCC singlet species bent by 148.6°and with substantial charge separation approaching Xe + C 2 -and a notably short (2.107 Å) Xe-C bond. The spectra of the Xe-13 C-12 C, Xe-12 C-13 C, and Xe-13 C-13 C 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 XeC 2 molecule. Laserinduced fluorescence studies reveal a near-IR emission likely due to XeC 2 but not yet understood. Infrared spectra in the Xe matrix reveal also formation of the HXeCCH molecule.

HXeCCH in Ar and Kr matrices

“…If H 2 molecules form upon photolysis, the formation of HXeCC needs global mobility of H atoms, which can be somewhat suppressed in the mixed matrices. Third, the Xe-CC molecule is computationally bent ͑148.6°͒, 30 which can produce a barrier for the formation of a linear HXeCC molecule, and this slows down the reaction at lower annealing temperatures in Ar and Kr matrices. We observed in solid Kr ͑C 2 H 2 /Xe/Kr͒ that the HCC and HCC¯Xe concentrations increase upon annealing.…”

Atypical compounds of gases, which have been called ‘noble’

“…In 2012 the semicentential will be celebrated for the discovery of the very first Ng compound. (v) Xe-C n where n = 2, 3, 5, 7, 9, 104,105 have been discovered, and the issue of stability of a hypothetical 1D polymer (-Xe-C 2 -), 106 was immediately addressed; 107 (vi) using the isoelectronic analogy between C 2 and BN, as the yet unknown and quite strongly bound species Xe-BN, Xe-NB, HXeNBH and HXeBNH 108 have been considered;…”

Selective and reversible control of a chemical reaction with narrow-band infrared radiation: HXeCC radical in solid xenon

“…The remaining barrier might originate from the differences in geometries of the XeC 2 molecule and the corresponding fragment in the HXeCC radical. Indeed, computationally the XeC 2 molecule is bent with an angle of 147°, 22 whereas HXeCC is linear. In this situation, the activation of the XeC 2 bending motion ͑computationally 87 cm −1 ͒ can contribute to the process.…”