Ultrafast Relaxation Dynamics in trans-1,3-Butadiene Studied by Time-Resolved Photoelectron Spectroscopy with High Harmonic Pulses

Abstract

In trans-1,3-butadiene, the ultrafast relaxation from the doubly excited state 2(1)Ag and the corresponding recovery of the ground state 1(1)Ag were observed simultaneously for the first time by time-resolved photoelectron spectroscopy (TRPES) using 29.5 eV high harmonic pulses. The fast recovery of 1(1)Ag shows that the following dissociation upon photoexcitation takes place after returning to the ground state. At 427 fs after photoexcitation, only the ionization energy from the C═C σ bond was found to remain shifted. Accompanying theoretical calculations with an assumption of Koopmans' theorem show that the ionization energy of the C═C σ bond is modulated by vibrational excitation of the antisymmetric C═C stretching mode. TRPES by high harmonics can probe the changes in the molecular structure sensitively.

Structural dynamics of photochemical reactions probed by time-resolved photoelectron spectroscopy using high harmonic pulses

“…25 The usage of ultrashort extreme ultraviolet (XUV) pulses by high harmonic generation enables us to probe not only the highest occupied MO (HOMO) but also lower-lying occupied MOs. [26][27][28][29][30] Lower-lying occupied MOs can be the ngerprints of the molecular structure, because each MO can be associated with each bonding nature, e.g. single bond, double bond, conjugated double bond, and so forth.…”

Understanding the modulation mechanism in resonance-enhanced multiphoton probing of molecular dynamics

“…The molecular relaxation generally leads to an increased ionization potential [7]. In order to detect the dynamics via a single-photon ionization (SPI) scheme, increased probe photon energies in the vacuum ultraviolet (VUV) [8][9][10][11][12][13] have been recently applied. Ex perimentally less demanding and therefore widely used is multiphoton ionization (MPI) [2,4,14,15], as shown for metal carbonyls [16,17] or nucleobases [18][19][20][21], As pointed out before, the transient MPI signal can be enhanced by resonant excited molecular states [14][15][16][17].…”

“…The two probing schemes, which are widely used in time-resolved experiments [2,[8][9][10][11][12][13][14][15][16][17][18][19][20][21], exhibit strong differences in their sensitivity to this relaxation processes. While photoelectron spectroscopy based on SPI does not show any modulation with pump-probe delay, the MPI shows a clear signal decay within 1 ps.…”

“…We therefore regard single-photon probing abetter method for a systematic investigation of underlying molecular dynamics. Although high-harmonic sources have only been used on conceptually simple molecules [8][9][10][11][12][13] so far, appli cation of SPI on more complex systems such as nucleobases, base pairs, and base-pair models [36] will be possible.…”

Time-Resolved Photoelectron Spectroscopy of Dissociating 1,2-Butadiene Molecules by High Harmonic Pulses

“…22 It has been suggested that these two dissociations take place after the internal conversion to the ground state. 22 Thus, we were interested in the ultrafast relaxation processes in 1,2-butadiene, which is a cumulated diene in contrast with 1,3-butadiene, 12 and were motivated to study the relatively simple bond-breaking dynamics by observing the dynamics of lowerlying occupied MOs.…”