Vibrational action spectroscopy of the C-H and C-D stretches in partially deuterated formic acid dimer

Vibrational action spectroscopy of jet-cooled formic acid dimer measures the frequency of the C-H(D) stretching vibration and its coupling to nearby states. The action spectrum of (DCOOH)(2) reveals a specific Fermi resonance between the C-D stretch and two antisymmetric combination states formed from the C-O stretch and DCO bend. A three-state deperturbation analysis shows that there is a relatively strong coupling between the fundamental vibration and each of the combination vibrations (vertical bar 13 cm(-1)vertical bar) as well as between the combination states themselves (vertical bar 7 cm(-1)vertical bar). This situation contrasts with that for the action spectrum of (HCOOD)(2), where the C-H oscillator is isolated and not strongly coupled to other states. (c) 2008 American Institute of Physics.