Exploring the Excited-State Dynamics of Hydrocarbon Radicals, Biradicals, and Carbenes Using Time-Resolved Photoelectron Spectroscopy and Field-Induced Surface Hopping Simulations

Abstract

Reactive hydrocarbon molecules like radicals, biradicals and carbenes are not only key players in combustion processes and interstellar and atmospheric chemistry, but some of them are also important intermediates in organic synthesis. These systems typically possess many low-lying, strongly coupled electronic states. After light absorption, this leads to rich photodynamics characterized by a complex interplay of nuclear and electronic motion, which is still not comprehensively understood and not easy to investigate both experimentally and theoretically. In order to elucidate trends and contribute to a more general understanding, we here review our recent work on excitedstate dynamics of open-shell hydrocarbon species using time-resolved photoelectron spectroscopy and field-induced surface hopping simulations, and report new results on the excited-state dynamics of the tropyl and the 1-methylallyl radical. The different dynamics are compared, and the difficulties and future directions of time-resolved photoelectron spectroscopy and excited state dynamics simulations of open-shell hydrocarbon molecules are discussed.

Excited state dynamics of normal dithienylethene molecules either isolated or deposited on an argon cluster

“…Unfortunately, without a full theoretical description in the spirit as the “field-induced surface hopping simulations” reported in ref. 29, it is difficult, if not impossible, to get convincing information from these data. Hence, only the total PE signal is considered here, i.e.…”

Photodissociation of the trichloromethyl radical: photofragment imaging and femtosecond photoelectron spectroscopy

“…Computationally, the neutral and ionic ground state have been investigated, 31,33 but information available on the excited electronic states is limited to low-level methods like Hartree-Fock. 28 In order to obtain a full picture of the excited-state dynamics of CCl3, we initiated a study that combines femtosecond-time resolved photoionisation and photoelectron spectroscopy (TR-PES) [34][35][36] to explore the initial processes following photoexcitation with nanosecond photofragment imaging 37,38 to monitor the photodissociation products. The latter approach has evolved into a method that provides detailed insight into the photodissociation mechanism of stable molecules [38][39][40] and radicals 41 by monitoring the translational energy release of photofragments.…”

Photodissociation of Benzoyl Chloride: A Velocity Map Imaging Study Using VUV Detection of Chlorine Atoms

“…Velocity map imaging (VMI) of photofragments is an efficient and versatile technique to study photodissociation as both translational energy and angular distribution of photofragments can be measured simultaneously with mass selectivity . Thus, the technique has been widely applied to study photofragmentation as well as reactive scattering, bimolecular reactions and time-resolved chemical dynamics. − In general, resonance-enhanced multiphoton ionization (REMPI) is applied for fragment detection, but in recent years, single photon ionization using VUV has also been used as a universal ionization source in multi mass ion imaging. − …”