Accurate measurement of the T-shaped and linear binding energies using vibronic-specific I2(B,ν) fragment velocity-map imaging

Vibrational predissociation versus intramolecular vibrational energy redistribution (IVR) in rare gas⋯dihalogen complexes: IVR identified in Ar⋯I2(B, ν') using velocity-map imaging

The competition between multiple pathways sampled during the energetic relaxation of excited molecules can be difficult to experimentally decipher. The rare gas···dihalogen van der Waals complexes have remained key systems for exploring the competition between relaxation pathways, such as intramolecular vibrational energy redistribution (IVR) and vibrational predissociation (VP). As these mechanisms can yield the same products, the relaxation pathways traversed are often deduced from the excitation spectra or product-state distributions. In addition to a brief perspective on IVR and VP in rare gas⋯dihalogen complexes, we present new results obtained using time-of-flight velocity-map imaging (VMI) on T-shaped Ar⋯I₂(B, ν', n' = 0) complexes that illustrate how contributions from these two pathways can be separated. The angular anisotropies of the ion images collected for the I₂(B, ν < ν') fragments indicate the products for certain Ar⋯I₂(B, ν', n' = 0) levels are weighted along the direction perpendicular to the laser-polarization axis. These distributions are consistent with prompt dissociation of the T-shaped excited-state complexes, likely via direct VP. The distributions measured for other Ar⋯I₂(B, ν', n' = 0) levels are preferentially along the laser-polarization axis. These initially prepared levels must undergo IVR with nearly resonant Ar⋯I₂(B, ν < ν', n > 0) intermolecular vibrational levels that sample linear Ar-I-I orientations during dissociation.

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.

The Halogen-Bond Nature in Noble Gas-Dihalogen Complexes from Scattering Experiments and Ab Initio Calculations

In order to clarify the nature of the halogen bond (XB), we considered the prototype noble gas–dihalogen molecule (Ng–X₂) systems, focusing on the nature, range, and strength of the interaction. We exploited data gained from molecular beam scattering experiments with the measure of interference effects to obtain a suitable formulation of the interaction potential, with the support of high-level ab initio calculations, and charge displacement analysis. The essential interaction components involved in the Ng–X₂ adducts were characterized, pointing at their critical balance in the definition of the XB. Particular emphasis is devoted to the energy stability of the orientational Ng–X₂ isomers, the barrier for the X₂ hindered rotation, and the influence of the X₂ electronic state. The present integrated study returns reliable force fields for molecular dynamic simulations in Ng–X₂ complexes that can be extended to systems with increasing complexity and whose properties depend on the selective formation of XB.

Investigations of the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) binary van der Waals complexes: ab initio intermolecular potential energy surfaces, vibrational states and predicted pure rotational transition frequencies

The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.