Vibrational excitation of the ν2 mode of NH3 by infrared free electron laser

Vibrational excitation process in NH3 by a mid-infrared free electron laser at Tokyo University of Science (FEL-SUT) is reported. The population of the ν2 = 1 and 2 vibrationally excited states was monitored by the (2 + 1) resonance-enhanced multi-photon ionization (REMPI) technique via the B∼1E″ Rydberg state. Excitation efficiency of the ν2 = 1 ← ν2 = 0 transition was approximately 30%. The rotationally resolved pathway for the vibrational ladder climbing up to ν2 = 2 was identified through the analyses of the REMPI spectra and the FEL excitation spectra.