Femtosecond ground state dynamics of gas phase N2O4 and NO2

Non-resonant femtosecond time-resolved four-wave mixing (FWM) data on gas phase NO2 and N2O4 are presented. The initial rotational dephasing is observed during the first picosecond after excitation. Fast vibrational dynamics (average value 133±1 fs beats) are observed for dinitrogen tetroxide and are assigned to the ν3 N–N stretching mode in the ground state (1Ag). Rotational revivals on the picosecond time scale are recorded for both samples. No evidence of a long-lived excited state participation was found using photon echo (PE) or virtual echo (VE) pulse sequences with 800 nm laser pulses, however, NO2 photoproducts were observed following N2O4 excitation.