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Sub-Doppler infrared spectroscopy and formation dynamics of triacetylene in a slit supersonic expansion.

Authors :
Chih-Hsuan Chang
Agarwal, Jay
Allen, Wesley D.
Nesbitt, David J.
Source :
Journal of Chemical Physics. 2016, Vol. 144 Issue 7, p1-10. 10p. 3 Charts, 6 Graphs.
Publication Year :
2016

Abstract

Infrared spectroscopy and formation dynamics of triacetylene are investigated in a slit jet supersonic discharge and probed with sub-Doppler resolution (≈60 MHz) on the fundamental antisymmetric CH stretch mode (?5). The triacetylene is generated in the throat of the discharge by sequential attack of ethynyl radical with acetyelene and diacetylene: (i) HCCH ? HCC + H, (ii) HCC + HCCH ? HCCCCH + H, (iii) HCC + HCCCCH ? HCCCCCCH + H, cooled rapidly in the slit expansion to 15 K, and probed by near shot-noise-limited absorption sensitivity with a tunable differencefrequency infrared laser. The combination of jet cooled temperatures (Trot = 15 K) and low spectral congestion permits (i) analysis of rotationally avoided crossings in the ?5 band ascribed to Coriolis interactions, as well as (ii) first detection of ?5 Π-Π hot band progressions built on the ?12 sym CC bend and definitively assigned via state-of-the-art ab initio vibration-rotation interaction parameters (αi), which make for interesting comparison with recent spectroscopic studies of Doney et al. [J. Mol. Spectrosc. 316, 54 (2015)]. The combined data provide direct evidence for significantly non-equilibrium populations in the CC bending manifold, dynamically consistent with a strongly bent radical intermediate and transition states for forming triacetylene product. The presence of intense triacetylene signals under cold, low density slit jet conditions provides support for (i) barrierless addition of HCC with HCCCCH and (ii) a high quantum yield for HCCCCCCH formation. Complete basis set calculations for energetics [CCSD(T)-f12/VnZ-f12, n = 2,3] and frequencies [CCSD(T)- f12/VdZ-f12] are presented for both radical intermediate and transition state species, predicting collision stabilization in the slit jet expansion to be competitive with unimolecular decomposition with increasing polyyne chain length. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00219606
Volume :
144
Issue :
7
Database :
Academic Search Index
Journal :
Journal of Chemical Physics
Publication Type :
Academic Journal
Accession number :
113247783
Full Text :
https://doi.org/10.1063/1.4940905