HF rotational laser emission through photoelimination from vinyl fluoride and 1,1-difluoroethene

Rotational laser emission by HF has been observed at 33 frequencies between 325 and 1250 cm−1 from the flash photolysis (1.2 μsec FWHM) of vinyl fluoride and of 1,1-difluorethylene. The transitions lie within the v = 0 to v = 5 manifolds and range from J″→J′ = 8→7 to 31→30. Increasing the atomic weight or the partial pressure of the inert buffer gas (He, Ne, or Ar) raises the gain of nearly all transitions, showing that collisional relaxation processes are active in pumping the laser emission. The high gains displayed by both precursors in the J = 14→13 transitions for the v = 0,1,2, and 3 manifolds indicate that V→R energy transfer is pumping molecules into the v′, J = 14 state from the near-resonant v′+1, J = 2, 3, and 4 states. In a similar way, the highest J transitions J = 31→30 to 28→27 with v = 0 and/or 1, are best explained by V→R energy transfer from near-resonant low-J states from much higher vibrational manifolds v′ = 4, 5, and 6. This would imply collision-induced multiquantum energy transfer with large Δv (up to Δv = 5) and large ΔJ (up to ΔJ = 26) or a rapid succession of steps with smaller Δv and ΔJ. In contrast, the high gains displayed by the J = 10→9 transitions in the v = 0, 1, and 2 manifolds are best explained in terms of R→T relaxation from a uniform nascent population. While there are indications that the nascent rotational distributions provided by these photoeliminations probably furnish population to high J states, the gain patterns indicate that the V→R and R→T energy relaxation processes are strongly influential, the former surely involving multiquantum steps with large ΔJ and probably with Δv>1 as well.