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Quantum beat frequency is the basis for understanding interference effects and vibrational wave packet dynamics and has important applications. Using femtosecond time-resolved mass spectrometry and femtosecond time-resolved photoelectron image combined with theoretical calculations, we study the electronic excited-state relaxation of o-fluoraniline molecule and the time-dependent evolution of vibrational wave packets between different eigenstates. After the molecule absorbs a photon of 288.3 nm and is excited to the S1 state, intramolecular vibrational redistribution first occurs on the time scale τ1 = 349 fs, and then the transition to the triplet state occurs through the intersystem crossing on the time scale τ2 = 583 ps, and finally, the triplet state occurs decays slowly through the time scale τ3 = 2074 ps. We find the intramolecular vibrational redistribution is caused by the 00, 10b1 and 16a1 vibrational modes of the Sl state origin. That is, the 288.3 nm femtosecond laser excites the molecule to the S1 state, and the continuous flow of the vibrational wave packet prepares a coherent superposition state of three vibrational modes. Through extracting the oscillation of different peak intensities in the photoelectron spectrum, we observe reversible changes caused by mutual interference of the S1 00, S1 10b1 and S1 16a1 states when the wave packets flow. When the pump pulse is 280 nm, the beat frequency disappears completely. This is explained in terms of increases in the vibrational field density and characteristic period of oscillation, and statistical averaging makes the quantum effect smooth and indistinguishable. In addition, the Rydberg component of the S1 state is more clearly resolved by combining experiment and theory. [ABSTRACT FROM AUTHOR]

Relaxation mechanism of S 1 state in UV excited Crotonaldehyde by femtosecond time-resolved photoelectron imaging combined with time-resolved mass spectrometry. In addition, the energy of several Rydberg states was obtained via accidental resonance with these Rydberg states in the process of multi-photon ionization combined with high level TD-DFT quantum chemical calculation. • Internal conversion was observed in the timescale of <100 fs. • The energies of 3 s and 3 p Rydberg states were obtained experimentally. • Quantum chemical calculation was performed on excited states. Real-time evolution of S 1 state crotonaldehyde is tracked by utilizing femtosecond time-resolved photoelectron imaging and time-resolved mass spectroscopy with UV excitation. Our experimental results show that crotonaldehyde molecule has experienced a quick internal conversion to the ground state in an ultrafast timescale of <100 fs following excitation to S 1 state both with 310 nm and 365 nm pumping. In addition, the energy of 3 s and different 3 p Rydberg states of crotonaldehyde were assigned to be 3 s = 6.98 ± 0.11 eV, 3 p y = 7.30 ± 0.08 eV, 3 p x = 7.63 ± 0.04 eV, and 3 p z = 7.79 ± 0.03 eV by combining the multi-peak time-resolved photoelectron spectroscopy and quantum chemistry calculation results. [ABSTRACT FROM AUTHOR]