Role of ion-pair states in the predissociation dynamics of Rydberg states of molecular iodine

Real-time dynamics of vibronic wavepackets within Rydberg and ion-pair states of molecular iodine

Real-time dynamics of vibrationally and electronically excited I2 molecules has been investigated experimentally using the pump-probe technique. A 2-photon excitation was performed either at 269 nm or 266 nm. An electronic and vibrational wavepacket was built as coherent superposition of a few (269 nm excitation) or many (266 nm excitation) Rydberg states of the and series partly coupled with ion-pair states. The probe operated by ionisation or photodetachement. The energy and angular distribution of the resulting photoelectrons, I+ photocations and I- photoanions were monitored. During the dynamics that is turned on by the pump excitation, the wavepacket splits and explores a variety of electronic states of Rydberg and ion-pair character. The experimental results were complemented by molecular dynamics calculations. This provided invaluable information to identify wavepacket motion along ion-pair potential energy curves.

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

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.

Predissociation Dynamics of Br2 in the [2Π1/2]c5d; 0g + and [2Π3/2]c6d; 0g + Rydberg States by Velocity Map Imaging Study

We investigated the predissociation dynamics from the [²Π_1/2]_c5d; 0_g ⁺ and [²Π_3/2]_c6d; 0_g ⁺ Rydberg states of Br₂ using the velocity map imaging technique. Two-dimensional scattering images of the fragmented Br⁺ exhibited an isotropic feature upon the excitation of these Rydberg states. Analysis of the total kinetic energy release suggested the existence of the predissociation pathways to the dissociation limits of Br(5s, ⁴P_3/2) + Br(4p, ²P_3/2) and Br(5s, ⁴P_5/2) + Br(4p, ²P_3/2) via the 0_g ⁺ ion-pair states that interact with the lower and/or excited-core Rydberg states lying at long internuclear distance regions thorough the avoided crossing.

Self-assembling of the neutral intermediate with chemically bound argon in photoexcited van der Waals complex Ar-I2

Photodissociation of the van der Waals complex Ar-I₂ after excitation into the Rydberg states of I₂ has been investigated with velocity map imaging of photofragments. Formation of the translationally hot ions of argon Ar⁺ with three modes in kinetic energy distribution has been revealed. The measured dependence of the kinetic energy of Ar⁺ on the pumping photon energy indicates the appearance of Ar⁺ from three channels of the photodissociation of the linear intermediate Ar⁺-I-I^- containing chemically bound argon. These channels are (1) dissociation into Ar⁺+ I₂ ^-; (2) three-body dissociation into (Ar⁺)* + I* + I^-, with (Ar⁺)* and I* being the ²P_1/2 states of the species; and (3) two-body electron photodetachment, giving rise to Ar⁺ + I₂ + e. Three indicated channels are similar to those established for the photodissociation of trihalide anions. This similarity confirms the conclusion on the formation of the Ar⁺-I-I^- intermediate, which is isoelectronic to the trihalide anion Cl-I-I^-. The mechanism of the Ar⁺-I-I^- formation involves two-photon excitation of the complex Ar-I₂ into the Rydberg state of I₂ converted into the ion-pair state and further electron transfer from Ar to I⁺ of the ion-pair state. The self-assembling of the structure making the formation of the Ar⁺-I-I^- intermediate energetically accessible is confirmed by modeling the dynamics in the excited linear complex Ar-I₂. Photoexcitation of the van der Waals complexes of noble gases with halogens into the ion-pair states of halogen is supposed to be a promising approach for generating the new chemical compounds of noble gas atoms.