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Published November 1, 2000 | public
Journal Article Open

Rovibrational spectroscopy of the v = 6 manifold in 12C2H2 and 13C2H2


We recorded rovibrational spectra of the 006+ level of 12C2H2 and the 2131 11–1 level of 13C2H2 in the ground electronic state using a two-photon sequential double resonance technique with a resolution of 15 MHz. Owing to the g/u symmetry of acetylene, the levels that we observe are inaccessible from the ground state by single photon techniques, and observation of these levels is reported here for the first time. Upper state rotational constants were derived from whole band fits of the observed lines, and compare favorably with expected values. Both spectra exhibit signs of local perturbations, and a density of states analysis leads us to believe that we are observing couplings to the full density of vibrational states one would expect from acetylene in this energy region. Despite the high resolution of our spectrometer, and the high excitation energy, no evidence for acetylene hydrogen permutation exchange isomerization (which is predicted to proceed through the vinylidene minimum on the potential) has been observed, implying that the rate of exchange isomerization is more than four orders-of-magnitude below the rate predicted by RRKM (Rice, Ramsperger, Kassel, and Marcus) theory.

Additional Information

©2000 American Institute of Physics. (Received 27 June 2000; accepted 28 July 2000) The authors wish to thank Paul Rabinowitz for the loan of a lock-in amplifier used in this experiment. This work was supported by the National Science Foundation under Grant No. CHE97-03604. R.W.F. and M.L.S. are grateful to the Department of Energy (Grant No. DE-FGO2-87ER-13671) for support of their research at MIT.


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