Semiempirical model is developed for studying the electronic structure of the rare gas atom–halogen molecule systems. It is formulated in the frame of diatomics‐in‐molecule (DIM) approach and takes explicitly into account strong spin–orbit coupling pertinent to heavy halogen molecules. The consistent DIM scheme is realized for intermolecular interactions, whereas the description of valence electronic states of halogen molecule is more approximate being based on the asymptotic wave functions. The corresponding perturbation theory is also put forward. The model is applied to analysis of several features of the Ar...I2 van der Waals complex. First, the calculations on the spectroscopic constants of the B←X transition in the complex reveal the quantitative performance of the model. Second, mechanisms of nonadiabatic dynamics are examined. The results are qualitatively consistent with the current view on the Ar...I2 electronic predissociation and one‐atom cage effect. Third, the prediction is made on the valence electronic spectrum of Ar...I2 complex. These examples demonstrate the reliability of the model.

Ar–I2 interactions: The models based on the diatomics‐in‐molecule approach

We review spectroscopic and photodissociation dynamical studies in the region of the B L X transition of the Ar ··· I 2 van der Waals complex, both below and above the dissociation limit of the state. This very simple system constitutes a prototype for a wide range of molecular processes: vibrational predissociation involving intramolecular vibrational relaxation, electronic predissociation, cage effect, . Each of these processes has been or still is the subject of differing interpretations: intramolecular vibrational relaxation involved in the vibrational predissociation of this system can be in the sparse or statistical regime, vibrational and electronic predissociation are in competition and a direct, ballistic interpretation of the cage effect as well as a non-adiabatic one have been proposed. The study of the dependence of these dynamical processes on the relative orientation of the two partners of the complex (stereodynamics) is made possible by the coexistence of two stable Ar ··· I 2 ) isomers. E...

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Ar ··· I2: A model system for complex dynamics

The approach-induced I2() transitions, M=He, Ar, I2, N2, CF4

Rotational and vibrational energy transfer rate constants have been measured for excited rovibrational levels of I2(X) Stimulated emission pumping was used to excite the levels v=23, J=57, and v=38, J=49 via the B–X transition Laser induced fluorescence from the D–X system was used to follow the collision dynamics Energy transfer processes induced by collisions with He,Ar,N2,O2,Cl2,I2, and H2O were investigated Rotational energy transfer was found to be efficient for all collision partners In accordance with classical models, the total rotational transfer rate constants were proportional to the collision momentum (except for H2O) The total transfer rate constants and the distributions of rotational levels populated by collisions were not dependent on the initial vibrational state For colliders that are not good quenchers of I2(B), the rotational energy transfer dynamics of the X and B states were found to be very similar For colliders that are good quenchers, comparisons of the X and B state dynam

Inelastic collision dynamics of vibrationally excited I2(X)

Rate constants for collisional transfer between highly excited levels of I2(X) have been measured. A single vibration–rotation state (v‘=42, J‘=17) was populated by stimulated emission pumping. The prepared level, and collisionally populated levels, were detected by laser excitation of the D–X system. Relaxation kinetics were determined by variation of the delay between the dump and probe laser pulses. Collisions with He, Ar, I2, and O2 were investigated. Rotational energy transfer rate constants were measured for all collision partners. Vibrational energy transfer (Δv=−1) was observed for He, and O2, but this process was immeasurably slow for Ar and I2.

Energy transfer rate constants for highly excited rovibrational levels of I2(X)

The previously published compilation of rate data for inelastic collision processes involving the homonuclear and heteronuclear diatomic halogen molecules [J. Phys. Chem. Ref. Data 13, 445 (1984)] has been updated through June, 1986. Additional data on collision processes involving the interhalogens, and on processes at very low kinetic temperatures, are presented; in addition, several previously accepted rate data have been corrected.

J. I. Steinfeld

Papers

Rate Data for Inelastic Collision Processes in the Diatomic Halogen Molecules. 1986 Supplement.