Ab Initio Study of Ion-Pair States of Halogen Molecules

• Published in: Russian Journal of Physical Chemistry A 2020-07, Vol.94 (7), p.1382-1395
• Main Authors: Alekseeva, S. V., Alekseev, V. A.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Correlation; Electron affinity; Electron spin; Electron transitions; Ion pairs; Mathematical analysis; Physical Chemistry; Self consistent fields; Spin dynamics; Structure of Matter and Quantum Chemistry
• ISSN: 0036-0244; 1531-863X
• DOI: 10.1134/S0036024420070043

The ion-pair states of IBr, ICl, and BrCl molecules correlating to the limits of dissociation X + ( 3 P 2,1,0 , 1 D 2 ) + Y – ( 1 S 0 ) are studied using a complete active space self-consistent field (CASSCF), allowing for dynamic electronic correlations and spin–orbit interaction. Using experimental results, the calculated values of the equilibrium energy of the X + Y − ( 3 P 2 ) states correlating to the lowest ion state X + ( 3 P 2 ) are grouped in the range Δ T e  ∼ 100 cm −1 , with the error of their relative location also on the order of 100 cm −1 . For most states, the difference between the experimental and calculated values of the equilibrium internuclear distance does not exceed – = 0.02 Å. A comparative analysis of structural features of the ion-pair states of homonuclear and heteronuclear halogen molecules is performed using results from recent ab initio calculations for the I 2 molecule. We also discuss some issues concerning ion-pair states X − Y + with inverted charge localization, which correlate to the limits of dissociation X – + Y + and are coupled with the X + Y − states by two-electron transitions. It is noted that the structures with two stable localizations of two electrons, X + ‒D‒Y − and X − ‒D‒Y + , where X, Y are electron affinity centers (atoms, molecules, clusters) and D is a dielectric spacer, could be of interest for microelectronics.