SUB-DOPPLER SLIT JET DISCHARGE SPECTROSCOPY OF JET COOLED POLYACETYLENES: THE ANTI-SYMMETRIC CH STRETCH MODE OF TRIACETYLENE

Abstract

Growth of polyacetylenic molecules in acetylene flames is thought to play a central role in combustion chemistry and formation of soot, as well as the chemistry of gas clouds in the interstellar medium. In this talk, we present results from first sub-Doppler, high resolution infrared spectroscopic studies on triacetylene.$^{,}$ In particular, we explore the fundamental anti-symmetric CH stretching mode ($v$$_5$) of jet-cooled triacetylene in a pulsed slit discharge, where the ${in-situ}$ synthesis arises from a discharge of trace(0.1-1\%) acetylene/rare gas mixtures followed by rapid CCH + HCCH chemistry in the supersonic expansion environment. The band origin of this mode is determined to be 3329.0544(2) cm$^{-1}$. At high resolution, a series of avoided energy level crossings arising from rotational perturbations are observed and ascribed to perpendicular Coriolis mixing with a near degenerate manifold of $\Pi$ vibrational symmetry. The energy level patterns are successfully analyzed to reveal spectroscopic constants and Coriolis coupling matrix elements for the perturbing manifold. In addition, a weak $\Pi$-$\Pi$ hot band progression due to thermal population in the slit jet is observed and assigned.