Approximate constants of motion and energy transfer pathways in highly excited acetylene

Approximate constants of motion of acetylene (C2H2), analyzed previously below 10 000 cm−1, are determined from analysis of a nonlinear least squares fit of the highly excited vibrational absorption spectrum. Although there are at least ten distinct Fermi resonance couplings in the measured spectrum up to 24 000 cm−1, there is one, and quite possibly two, good constants of motion. These constants are pointed out to be equivalent to a preferred energy transfer pathway discussed by Smith and Winn. It is suggested that these constants may also apply to ‘‘unassignable’’ stimulated emission pumping spectra, which sample a different region of phase space.