Interaction-induced electric properties George Maroulis* DOI: 10.1039/9781849734790-00025 1 Introduction The basic aspects of the theory of electric polarizability are widely recog- nized as of fundamental importance to the rational approach and inter- pretation of large classes of phenomena. 1 In particular, these properties are of fundamental importance to intermolecular interaction studies, 2 nonlinear optics, 3–5 scattering 6 and the simulation of fluids. 7,8 Electric properties are of importance to the modeling of solvation properties. 9 General molecular characteristics as hardness, 10 softness, 11 hypersoftness, 12 stiffness 13 and compressibility 14 are now systematically linked to electric polarizability and hyperpolarizability. Understandably, polarizability is also linked to reac- tivity. 15 The dipole moment, polarizability and hyperpolarizability are powerful molecular descriptors that find use in quantitative structure- property (QSPR) or structure activity (QSAR) relationships. 16 Interest extends also to electric moments higher than the dipole, as evidenced by a recent study on the toxicity of polychlorinated of dibenzofuranes. 17 Con- siderable progress and interest in electric polarizability is now obvious in studies focused on the understanding of pharmacological activity. 18–21 The term interaction-induced polarizability, sometimes also called excess polarizability, signifies the effect caused by the interaction of two molecular systems. This property is of central importance to the analysis and inter- pretation of spectroscopic observations in collision- and interaction-induced spectroscopy. A particularly rich introduction to early efforts in field is available to reader in two fine, classic collections of papers, Phenomena Induced by Intermolecular Interactions, edited by Birnbaum 22 and Collision- and Interaction-Induced Spectroscopy, edited by Tabisz and Neuman. 23 We also recommend two magisterial texts, Collision-induced absorption in gases by Frommhold 24 and Collisional Effects on Molecular Spectra: Laboratory experiments and models, consequences for applications by Hartmann et al. 25 The aim of this review is to collect significant, recent the most, con- tributions to the calculation of interaction-induced electric properties. Explicit presentation of theoretical work and experimental efforts is rather beyond the scope of this text. Nevertheless, we present in this Introduction a selection of papers that brings forth important and practical aspects of the interplay of collision-induced spectroscopy and the theory and calculation of interaction-induced electric properties. Hunt reported a model that predicts long range, dipoles, quadrupoles and hyperpolarizabilities for interacting inert-gas atoms. 26 Among other examples Hunt calculates the long-range quadrupole moment of homo- nuclear atom pairs as Department of Chemistry, University of Patras, GR-26500 Patras, Greece. E-mail: maroulis@upatras.gr Chem. Modell. , 2012, 9, 25–60 | 25  c The Royal Society of Chemistry 2012 Downloaded by UNIVERSITY OF PATRAS on 13 February 2013 Published on 23 October 2012 on http://pubs.rsc.org | doi:10.1039/9781849734790-00025