Femtosecond pump-probe photoelectron spectroscopy of predissociative Rydberg states in acetylene

We employ a pump-probe approach to molecular photoionization to study fast dissociation of Rydberg states in acetylene. By using time-resolved photoel ectron spectroscopy to study the electronic state of the resulting ions we are able to monitor the system continuously during dissociation or rearrang ement. We find that the predissociative lifetime for the 3R(''') (v(2)(')=1 ) Rydberg state is about 150 fs. We demonstrate a powerful new technique us ing time-correlated femtosecond harmonic generation and laser light pulses to study the time evolution of ultrafast dynamic processes in molecules. (C ) 2000 American Institute of Physics. [S0021-9606(00)01717-7].