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Structure rearrangement processes, such as isomerization, are attracting extensive interest as a potential carrier in molecular scale electronics design. UV-light-triggered isomerization of Rydberg-excited propanal with two UV photons has been investigated with time-resolved photoelectron spectroscopy. By following the photoionization from 3s Rydberg states in the time domain, the ultrafast structural evolution and the corresponding photoisomerization dynamics are observed and tracked in real-time. The conversion barrier for isomerization from cis-propanal to gauche isomer is estimated to be about 1500 ± 100 cm−1 experimentally. Both the photoisomerization yield and the conversion rate have shown strong dependence on the excitation energy. It is observed that whether vibration modes are selectively excited or not, cis-to-gauche photoisomerization of propanal in 3s Rydberg state occurs once the excitation energy is higher than the conversion barrier without any vibrational excitation specificity. This yields a powerful approach to studying structural evolution dynamics in large molecules, which may have applications in molecular devices. [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]