ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Coherent anti-Stokes Raman spectroscopy has been used to study C2H6 in the rotational and ν3 CC stretching regions. Pure rotational transitions for torsionally excited molecules are seen for the first time and direct analysis of the peak maxima gives B values of 0.663 06 and 0.660 37 cm−1 for the υ4=0 and 1 torsional levels. The change in B is combined with ab initio calculations to show that the primary response of the molecule to the increased torsional amplitude is a CC extension of 0.0031 A(ring), plus a slight increase of 0.10 degrees in the CCH angle. For the ν3 vibrational Q branch, a complex mixture of four band systems is seen, a consequence of Fermi resonance interactions causing the predicted four torsional sublevels of this state to separate. Spectra of jet-cooled samples aid in the assignment of the spectrum and the four torsional components are determined as 994.973 (E3s), 994.878 (E3d), 994.864 (A1s), and 993.791 cm−1 (A3d). The A and B rotational constants decrease by 0.003 27 and 0.006 21 cm−1, respectively, when ethane is excited in the ν3 mode. These differences are used with the ab initio results to deduce that this transition results in a net increase of 0.010 A(ring) in the average CC distance, accompanied by a decrease of 0.12 degrees in the CCH angle and a very small CH decrease of 0.0002 A(ring). The calculations also suggest that the V3 torsional barrier for the υ3=1 state is about 3% smaller than for the ground state.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.464658
Permalink
