Photoionization and Photofragmentation Dynamics of I₂ in Intense Laser Fields: A Velocity-Map Imaging Study

Abstract

The photoionization and photofragmentation dynamics of I2 in intense femtosecond near-infrared laser fields were studied using velocity-map imaging of cations, electrons, and anions. A series of photofragmentation pathways originating from different cationic electronic states were observed following single ionization, leading to I+ fragments with distinct kinetic energies, which could not be resolved in previous studies. Photoelectron spectra indicate that these high-lying dissociative states are primarily produced through nonresonant ionization from several molecular orbitals (MO) of the neutral. The photoelectron spectra also show clear signatures of resonant ionization pathways (Freeman resonances) to low-lying bound ionic states via Rydberg states of the neutral moiety. To investigate the role of these Rydberg states further, we imaged anionic products (I–) formed through ion-pair dissociations of neutral molecules excited to these Rydberg states by the intense femtosecond laser pulse. Collectively, these results shed significant new light on the complex dynamics of I2 molecules in intense laser fields and on the important role of neutral Rydberg states in a full description of strong-field phenomena in molecules.

Two-Dimensional Projected-Momentum Covariance Mapping for Coulomb Explosion Imaging

“…The experimental apparatus consists of a Ti:sapphire laser system (Spectra-Physics Solstice Ace) coupled to a velocity-map imaging 42 (VMI) spectrometer. The setup has been described in detail in a prior publication, 43 hence only a brief overview is provided here. A ∼10% mixture of each sample was prepared by diluting its room temperature vapor pressure in helium, up to a pressure of 3 bar.…”

Stark control of multiphoton ionization through Freeman resonances in alkyl iodides

“…13 Their study in molecules presents an added level of complexity due to the possibility of vibrational excitation in both intermediate and ionic states. There have been relatively few studies on highly symmetric molecules, such as molecular hydrogen (H 2 ), 14 iodine (I 2 ), 15 ammonia (NH 3 ), 16,17 and methyl iodide (CH 3 I). [18][19][20] In the present study, we aimed to take this research one step forward by analyzing the relationship between the molecular structural complexity and the loss of symmetry in the generation of Freeman resonances.…”