Exploring wavepacket dynamics behind strong-field momentum-dependent photodissociation in CH2BrI+

Abstract

The ultrafast photodissociation dynamics of CH(2)BrI(+) into CH(2)Br(+) + I is studied using high level ab initio electronic structure calculations in conjunction with integration of the time-dependent Schrödinger equation and compared with measured pump-probe signals. These pump-probe measurements provide evidence for momentum-dependent dissociation, which is interpreted using two theoretical models. The first is based on DFT and TD-DFT calculations neglecting spin-orbit coupling, while the other, more rigorous model employs a larger number of coupled multi-configurational potentials obtained by means of CASSCF calculations. The latter model highlights the role of spin-orbit coupling between ionic electronic states as well as the effect of strong fields in the quantum dynamics including Stark-shifts and multi-photon excitation.

Strong-Field Molecular Ionization from Multiple Orbitals

“…For this molecule, at short delays one expects a maximum in the angle resolved parent-ion yield at zero degrees, given the S 0 -S 1 TDM and molecular orbitals [38]. Our measurements agree with this expectation.…”

Ionic dynamics underlying strong-field dissociative molecular ionization

“…For simulating the dynamics in CH 2 IBr + , the molecular parameters (potential energy curves, spin-orbit couplings and transition-dipole moments) are taken from Ref. [34]. Previous simulations with these parameters are in excellent agreement with the results of pump-probe measurements.…”

Pulse-shape-dependent strong-field ionization viewed with velocity-map imaging

“…The normal mode vibrational coordinate of the parent cation in its ground electronic state was also determined with the same method. As pointed out in previous publications [25,26], strong field ionization of CH 2 BrI by a near infrared (IR) ∼30 fs laser pulse induces a vibrational wave packet in the I-C-Br bending mode in the ground electronic state of CH 2 BrI + . With a simple one-dimensional model we were able to describe the time-dependent formation of CH 2 Br + by a probe pulse as the wave packet oscillates on the ground ionic state surface and comes into resonance with higher lying dissociative states [26].…”

“…As pointed out in previous publications [25,26], strong field ionization of CH 2 BrI by a near infrared (IR) ∼30 fs laser pulse induces a vibrational wave packet in the I-C-Br bending mode in the ground electronic state of CH 2 BrI + . With a simple one-dimensional model we were able to describe the time-dependent formation of CH 2 Br + by a probe pulse as the wave packet oscillates on the ground ionic state surface and comes into resonance with higher lying dissociative states [26]. In this model, the potential energy curves for the lowest five ionic states and for the ground state of the neutral molecule along the I-C-Br bending normal mode coordinate u were computed with the state-averaged complete active space self-consistent field (SA-CASSCF) method [27] with the MOLCAS 7.2 program package [28].…”