Femtosecond dynamics of the 2-methylallyl radical: A computational and experimental study

Abstract

We investigate the photodynamics of the 2-methylallyl radical by femtosecond time-resolved photoelectron imaging. The experiments are accompanied by field-induced surface hopping dynamics calculations and the simulation of time-resolved photoelectron intensities and anisotropies, giving insight into the photochemistry and nonradiative relaxation of the radical. 2-methylallyl is excited at 236 nm, 238 nm, and 240.6 nm into a 3p Rydberg state, and the subsequent dynamics is probed by multiphoton ionization using photons of 800 nm. The photoelectron image exhibits a prominent band with considerable anisotropy, which is compatible with the result of theory. The simulations show that the initially excited 3p state is rapidly depopulated to a 3s Rydberg state, from which photoelectrons of high anisotropy are produced. The 3s state then decays within several 100 fs to the D (nπ) state, followed by the deactivation of the D to the electronic ground state on the ps time scale.

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

“…In Ref. 93 we provide benchmark data on 2MA, confirming the experimentally established sequence of states n, 3s, bright 3p. At slightly higher energies, we found the two remaining and almost dark Rydberg 3p states.…”

“…At higher energies, a strong band is observed around 5.1-5.4 eV 92,96-98 , which is identified as a bright 3p Rydberg state 92,93 , similar to the case of allyl, albeit slightly red-shifted. A similar bright band has been found for 1MA between 5.2-5.4 eV 97 .…”

“…In the left part, the data of 2MA published in Ref. 93 are shown, while on the right, we present previously unpublished results for a mixture of (Z/E)-1MA, obtained using the same experimental setup as described in Ref. 93 .…”

“…The states C and D have been assigned as two 3p Rydberg states lying in the molecular plane, which are dark or only weakly allowed in one-photon absorption 73,82,84 . The bright E ( 2 B1) state is centered around 5.5 eV 73,92,93 and has been identified as a 3p Rydberg state perpendicular to the allyl plane 73,84 . Several higherlying Rydberg states, close to the experimental IP of 8.14 eV 70 have also been reported 70 .…”

Ultrafast Molecular Spectroscopy Using a Hollow-Core Photonic Crystal Fiber Light Source

“…Time-resolved photoelectron imaging (TRPEI) is a powerful variant of this general approach, yielding highly differential energy-and angle-resolved information that offers deep insight into the complex molecular photophysics. [8][9][10][11][12][13][14][15][16] A key requirement for time-resolved electronic spectroscopy is the generation of broadly tuneable UV femtosecond pulses. Commercial femtosecond laser systems, however, typically produce output centred in the near infrared (NIR).…”