Ultrafast curve crossing dynamics through conical intersections in methylated cyclopentadienes.
We explored the curve crossing dynamics of 1,2,3,4-tetramethyl-cyclopentadiene (TMCPD) and 1,2,3,4,5-pentamethyl-cyclopentadiene (PMCPD) upon pi --> pi* excitation to the 1B(2) state using time-resolved, resonance-enhanced multiphoton ionization mass and photoelectron spectroscopy. Upon excitation with a femtosecond laser pulse at 267 nm, the energy relaxation pathway is observed by a time-delayed probe pulse at 400 nm, which ionizes the molecule through Rydberg states that reveal the momentary state of the molecule in the photoelectron spectra. We observe that the initially populated 1B(2) state decays to the 2A(1) surface in 135 fs in TMCPD and 183 fs in PMCPD, followed by a crossing to the ground state 1A(1) surface on 57 and 60 fs time scales for TMCPD and PMCPD, respectively. The spectroscopic signatures of the 2A(1) states are clearly revealed in the two-photon ionization photoelectron spectra. In both systems we observe that the ground states are recovered completely, indicating that no new molecular structures are created on the time scale of the experiment.
Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Fedor
F
Rudakov
Peter M
PM
Weber
D003517:Cyclopentanes / Q000737:chemistry*; D008745:Methylation; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D056951:Photoelectron Spectroscopy; D017785:Photons; D021241:Spectrometry, Mass, Electrospray Ionization; D013997:Time Factors
C550293:1,2,3,4,5-pentamethyl-cyclopentadiene; C550294:1,2,3,4-tetramethyl-cyclopentadiene; D003517:Cyclopentanes