Detection of vibrationally hot NO and CO excited by infrared free electron laser

This paper describes preliminary results on the detection of vibrationally hot NO and CO molecules populated by light pulses from the free electron laser at Tokyo University of Science (FEL-SUT). For NO, FEL is tuned to 5.33 µm corresponding to the X2Π1/2(v''=1) ← (v''=0) transition. The population of the vibrationally excited state is probed by the (2 + 1) resonance enhanced multiphoton ionization (REMPI) technique via the 4sσ E2Σ+(v'=2) Rydberg state. For CO, 4.67 µm output from FEL-SUT excites the X1Σ+(v''=1) state which is subsequently ionized by (2 + 1) REMPI via the 3sσ B1Σ+(v'=1) Rydberg state. In both diatomic molecules, we succeeded in recording the excitation spectra associated with the v''=1 level with a good signal-to-noise ratio.