Selective two-stage excitation of an electronic state of organic molecules in aqueous solution by picosecond light pulse

An electronic state of rhodamine B dissolved in D₂O was excited, via an intermediate vibrational state, by the simultaneous action of infrared and visible frequency-tunable ultrashort pulses. The intermediate state was the first overtone of the valence asymmetric vibration of the methy 1 group CH₃ at the frequency of 5820 cm^–1. The spectrum of a weak overtone vibration was recorded by tuning the infrared pulse frequency.