Rotational laser emission from high J states of HF in the range 800-1100 cm-1 (v=0, J=22→21 to J=33→32; v=1, J=23→22 to J=29→28; and v=2, J=24→23 and J=25→24) has been initiated through flash photolysis of ClF: H2: Ar=2:1:23 mixtures at 63 Torr. The short threshold time (2-4 μsec) indicate that V→V up-pumping in HF‡-HF‡ collisions followed by V→R energy transfer cannot satisfactorily explain the observed emissions. The reaction H+ClF→HF+Cl must be involved in the pumping process, even though the branching ratio favors formation of HCl instead of HF. Two mechanisms are proposed and both could be operative. The rotationally excited HF that emits may be formed directly, as has been proposed by Polanyi and co-workers for this and other H+XY reactions on the basis of chemiluminescence results. It is also possible that multiquantum V→R energy transfer contributes population to the high J states. While HF and argon collision partners may participate in such pumping, the ClF molecule may be particularly effective because its closely spaced rotational levels allow near resonant energy transfer paths. © 1979 American Institute of Physics.