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 S_l 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.

Clarifying the relationship between conformation and charge transfer is crucial for understanding the functional mechanisms of molecules in organisms. Theoretical calculations of dopamine, N,N-dimethyldopamine, and N,N-dihydroxydopamine were related to conformation and charge transfer, and the charge transfer of the excited state was clearly characterized. First, the stable configuration of the ground state of the molecule was optimized, and the potential energy of the ionic state was scanned to select all conformations, except for the chiral problem. Subsequently, the CAM-B3LYP/aug-cc-pVTZ method was used to excite the molecule, and the excitation types of the first five excited states of the molecule were discussed. Finally, the charge transfer of the molecule was calculated, and the charge transfer of the different conformations was analyzed in detail. Through charge transfer, it has been speculated that dopamine molecules exist in a coiled state in an organism and interact with water to form N,N-dihydroxydopamine, or hydrogen bonds for better information transmission.