Prereactive evolution of monoalkenes excited in the 6 eV region

Abstract

Articles you may be interested inEffect of chemical substitutions on photo-switching properties of 3-hydroxy-picolinic acid studied by ab initio methods J. Chem. Phys. 140, 084301 (2014); 10.1063/1.4865815 On the origin of ultrafast nonradiative transitions in nitro-polycyclic aromatic hydrocarbons: Excited-state dynamics in 1-nitronaphthalene J. Chem. Phys. 131, 224518 (2009); 10.1063/1.3272536Mass-analyzed threshold ionization study of vinyl bromide cation in the first excited electronic state using vacuum-ultraviolet radiation generated by four-wave mixing in HgThe time evolution of the first excited states of ethylene, and alkyl substituted ethylenes, isomers with formula C 6 H 12 , has been studied by the femtosecond pump probe method, using mass spectrometric detection, in the region of 6 eV ͑200 nm͒. Two cyclic alkenes of the formula C 6 H 10 have also been studied. These systems exhibit a multi-exponential decay characterized by a very short time decay, ranging from 20 fs͑ethylene͒ to 100 fs ͑trans hex-2-ene͒ and a longer decay, in the picosecond range follows for most of the alkyl isomers. The short time evolution is characteristic of wave packet motion on a steep potential surface. The initial motion has been identified as the torsion about the CC double bond resulting from excitation of the valence state. The evolution of the valence excited state of excited state ethylene ͓first studied by the group of Radloff, Chem. Phys. Lett. 288, 2044 ͑1997͔͒ has been taken as a reference. The extremely rapid evolution, 20 fs, without any longer temporal component is explained by the disappearance of the wave packet from the Franck-Condon region into a conical intersection leading to the ground state surface by reference to the theoretical calculations of Ohmine ͓J. Chem. Phys. 83, 2348 ͑1985͔͒. This motion is essentially multidimensional to reach the funnel to the ground state; it combines the torsion about the CC double bond with a pyramidalization about one of the carbon atoms and/or H atom migration from one carbon to the other. Cyclic alkenes exhibit a similar behavior as ethylene with a single ultrashort decay that arises from this same mechanism. Also in the other substituted alkenes the short decay has been assigned to the wave packet motion away from the Franck-Condon region under the influence of the torsion about the double bond. The final longer decay could also be captured in the case of tetramethylethylene by a 800 nm probe as the internal conversion to the ground state via a funnel more difficult to reach. These measurements emphasize the role of conical intersections which could not be brought into evidence without time dependent methods.

Photoinduced dynamics of ethene in the N, V, and Z valence states: A six-dimensional nonadiabatic quantum dynamics investigation

“…Since the equilibrium geometry of the cation is only weakly twisted, 50 it is plausible that strongly twisted ethene molecules cannot be ionized with the probe pulses employed in the experiments. 48,49 The measured lifetimes are indeed in good agreement with the calculated time scale of twisting of ethene in the V state ͑cf. Fig.…”

Substituent Effects on Dynamics at Conical Intersections: Cyclopentadienes

“…Systematic chemical substitutions were used to discern the roles of electronic structure, density of states, and floppiness or rigidity in electronically nonadiabatic dynamics in substituted benzenes 8 and ethylenes. 9 Further studies on a substituted ethylene directly revealed vibrational wavepacket motions induced by passage through a conical intersection. 10 In a recent, detailed study on excited state dynamics in the R, -enones, 11 the location of a methyl substituent on acrolein (2-propenal) was shown to lead to very different photodynamics, despite the relative energetics and topologies of the CI's being very similar for all molecules concerned.…”

Ultrafast Electronic Relaxation of Excited State of Biomimetic Metalloporphyrins in the Gas Phase

“…Time dependent spectroscopy can probe very fast relaxation processes immediately after excitation with a resolution determined only by the autocorrelation time of the pump and probe pulses. Electronic relaxation, resulting from non adiabatic couplings between the electronic states involved, is effected via a wavepacket motion after the ultrafast excitation (Mestdagh et al, 2000). The wavepacket goes through the funnels of the conical intersections into the surfaces of lower electronic states.…”