An Isotopic Substitution Test for Orbiting H Atoms in Vibrationally Highly Excited X~1Σ+g Acetylene

International audienceA Statistical Fouurier Transform (SFT) analysis of the Stimulated Emission Pumping (SEP) spectrum of acetylene (at-26,500cm−1 above the zero-point energy of the X~1Σg state) revealed recurrences at 6 ps. A speculative assignment [J. P. Pique, M.Lombardi, Y. Chen, R. W. Field and J. L. Kinsey, Ber. Bursenges. Phys. Chem., 92, 422 (1988)] of these recurrences as a free orbiting motion of one H about CCH can be tested by isotopic substitution. We are recording SEP spectra of DCCD. Well isolated and rotationally assigned intermediate rovibronic levels for SEP have been selected from rotationally-resolved fluorescence excitation spectra (A~←X~,340) of C2D2 observed at different temperatures (−10K→400K). SEP spectra of vibrationally highly excited (>26,000cm−1 in X~1Σ+g state) C2D2 are currently being obtained through several low-J intermediate states. Each of these SEP spectra belongs to a nearly ``pure sequence'' of all rigorous quantum numbers (J. ortho/para etc.). The vibrational features in the congested spectral region sampled by SEP, however, are intrinsically unassignable in terms of the nonrigorous vibrational quantum numbers. We have applied a Statistical Fourier Tranform technique to decode the short-time (