Enhancement of strong-field multiple ionization in the vicinity of the conical intersection in 1,3-cyclohexadiene ring opening

Abstract

Nonradiative energy dissipation in electronically excited polyatomic molecules proceeds through conical intersections, loci of degeneracy between electronic states. We observe a marked enhancement of laser--induced double ionization in the vicinity of a conical intersection during a non--radiative transition. We measured double ionization by detecting the kinetic energy of ions released by laser--induced strong--field fragmentation during the ring--opening transition between 1,3--cyclohexadiene and 1,3,5--hexatriene. The enhancement of the double ionization correlates with the conical intersection between the HOMO and LUMO orbitals.

Strong-Field Dissociative Double Ionization of Acetylene

“…Our results on the one hand demonstrate that the two-body fragmentation channels are governed by the removal of electrons from the lower-lying molecular orbitals; on the other hand, they experimentally verify the central role of the electron localization-assisted enhanced ionization mechanism in the strong-field deprotonation ionization of acetylene. Our present work will shed some light on the understanding and controlling of the rich electron-nuclear dynamics of complex polyatomic, in particular hydrocarbon, molecules [15][16][17][18][41][42][43][44][53][54][55] in strong laser fields. …”

Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and ab Initio Study

“…Cyclohexa-1,3-diene (CHD) is one of the most thoroughly studied molecules in time resolved photoexcitation experiments [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and ab initio computations 9,15,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] and is the subject of two recent reviews. 32,33 The large interest originally stems from CHD being the prototype for a pericyclic reaction used to explain the Woodward-Hoffmann rules.…”

Probing ultrafast electronic and molecular dynamics with free-electron lasers

“…More detailed analysis of the fragment distribution patterns in the strong-field case reveals that the delayed transient increase in the energetic fragments is correlated with formation of the dication CHD 2+ [83,85]. This delayed enhancement in the cross section for double ionization occurs during the passage of the molecular geometry through the vicinity of a known conical intersection between the ground and first excited states in the molecule [83,85].…”

“…The same motif appears in important biochemical processes such as vitamin D synthesis. The CHD/HT isomerization has received significant attention in experiments and calculations that seek to investigate the role that the nonBorn-Oppenheimer interactions play in the photorelaxation [24,75,[77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96]. It is now known that the ring opening is complete in less than 200 fs, as a result of nonradiative relaxation through a conical intersection between the S 1 and S 0 states [75,81,84].…”