Chemical probing spectroscopy of H3+ above the barrier to linearity.

We have performed chemical probing spectroscopy of H(3) (+) ions trapped in a cryogenic 22-pole ion trap. The ions were buffer gas cooled to approximately 55 K by collisions with helium and argon. Excitation to states above the barrier to linearity was achieved by a Ti:sapphire laser operated between 11 300 and 13 300 cm(-1). Subsequent collisions of the excited H(3) (+) ions with argon lead to the formation of ArH(+) ions that were detected by a quadrupole mass spectrometer with high sensitivity. We report the observation of 17 previously unobserved transitions to states above the barrier to linearity. Comparison to theoretical calculations suggests that the transition strengths of some of these lines are more than five orders of magnitude smaller than those of the fundamental band, which renders them-to the best of our knowledge-the weakest H(3) (+) transitions observed to date.