High resolution absorption spectroscopy of the v1 = 2 - 6 acetylenic overtone bands of propyne: Spectroscopy and dynamics

Abstract

The rotationally resolved nv1 (n = 2 - 6) overtone transitions of the CH acetylenic stretching of propyne (CH3-C≡C-H) have been recorded by using Fourier transform spectroscopy (n = 2), various intracavity laser absorption spectrometers (n = 3, 4, and 6) and cavity ring down spectroscopy (CRDS) (n = 5). The 2v1, 3v1, and 6v1, bands exhibit a well-resolved and mostly unperturbed J-rotational structure, whose analysis is reported. The 5v1 band recorded by pulsed CRDS shows an unresolved rotational envelope. In the region of 12 700 cm-1, an anharmonic interaction is confirmed between 4v1 and 3v1 + v3 + v5. The band at a higher wave number in this dyad exhibits a partly resolved K-structure, whose analysis is reported. The mixing coefficient of the two interacting states is determined consistently using different procedures. The 1/35 anharmonic resonance evidenced in the 4v1 manifold induces weaker intensity borrowing from the 2v1 and 3v1 levels to the v1 + v3 + v5 and 2v1 + v3 + v5 level, respectively, which have been predicted and identified. Several hot bands around the 2v1, 3v1, and 3v1 + v3 + v5 bands arising from the v9 = 1 and v10= 1 and 2 bending levels are identified and rotationally analyzed, also leading to determine x1,9 [-20.3(3) cm-1], x1,10 [-1.7975(75) cm-1], and x3,10 [-6.56 cm-1]. The J-clumps of the P and R branches in the 6v1 band at 18 499 cm-1 show a Lorentzian homogeneous profile mostly J-independent with an average full width at half maximum (FWHM) of 0.17 cm-1, attributed to arising from the intramolecular vibrational energy redistribution towards the bath of vibrational states. A detailed comparative examination of the fine structure in all investigated nv1 (n = 2 to 7) overtone bands and the similar behavior of the cold and hot bands arising from v10= 1 definitively suggests that a highly specific low-order anharmonic coupling, still unidentified, dominates the hierarchy of interaction mechanisms connecting the nv1 levels to the background states. © 1999 American Institute of Physics.