The Advanced Research Workshop entitled "Weakly Interacting Molecular Pairs: Unconventional Absorbers of Radiation in the At- sphere" was held in Abbaye de Fontevraud, France, from April 29 to May 3, 2002. The meeting involved 40 researchers from 14 countries. The goal of this meeting was to address a problem that the scienti?c community is aware of for many years. Up now, however, the so- tion for this problem is far from satisfactory. Pair e?ects are called unconventional in the title of this meeting. In speci?c spectral domains and/or geophysical conditions they are recognized to play a dominant role in the absorption/emission properties of the atmosphere. Water vapor continuum absorption is among the most prominent examples. Permanently improving accuracy of both laboratory studies and ?eld observations requires better knowledge of the spectroscopic features - tributable to molecular pairs which may form at equilibrium. The Workshop was targeted both to clarify the pending questions and, as far as feasible, to trace the path to possible answers since the underlying phenomena are yet incompletely understood and since a reliable theory is often not available. On the other hand, the lack of precise laboratory data on bimolecular absorption is often precluding the construction of reliable theoretical models. Ideally, the knowledge accumulated in the course of laboratory studies should correlate with the practical demands from those who are carrying out atmospheric ?eld measurements and space observations.

I Theory.- Spectra of Two- and Three-Body Van Der Waals Complexes.- Bimolecular Absorption in Atmospheric Gases.- Trajectory Study of CO2?Ar And CO2?He Collision Complexes.- Theoretical Study of Interaction Potential and Pressure Broadening of Spectral Lines for the He?CH3F Complex.- Variational Solution of Anharmonic Vibrational Problems for Polyatomics and Molecular Pairs.- Interference Effects in the Infrared Spectrum of HD.- Collision-Induced Absorption in Dipolar Molecule-Homonuclear Diatomic Pairs.- Clustering, Saturated Vapors, And The Atmosphere: The (H2O)n, H2O-N2, and H2O-O2 Cases.- Equilibrium Constants for the Formation of Weakly Bound Dimers.- Collision Induced Far Wings of CO2 and H2O Bands in Ir Spectra.- Far-Wing Line Shapes: Application to the Water Continuum.- II Laboratory Studies.- Collision-Induced Absorption in the CO2 Fermi Triad for Temperatures from 211 K to 296 K.- Laboratory Studies of Oxygen Continuum Absorption.- Molecular Beam Scattering Experiments on Species of Atmospheric Relevance: Potential Energy Surfaces for Clusters and Quantum Mechanical Prediction of Spectral Features.- Collision-Induced Absorption of Gaseous Oxygen in the Herzberg Continuum.- Absorption Cross-Section of the Collision-Induced Bands of Oxygen from the UV to the Nir.- Cavity Ring-Down Spectroscopy of O2-O2 Collisional Induced Absorption.- Laboratory Fourier Transform Spectroscopy of The Water Absorption Continuum From 2500 To 22500 to 22500 cm?1.- Infrared Spectra of Weakly-Bound Complexes and Collision-Induced Effects Involving Atmospheric Molecules.- The Far-Infrared Continuum in the Spectrum of Water Vapor.- Resonator Spectroscopy as a New Method of Investigation of Unconventional Millimeter-Wave Atmospheric Absorbers.- III Atmospheric Applications.-Look-Up Table and Interpolation Methods For Radiative Transfer Calculations in the Infrared Application to Balloon and Satellite Spectra.- The Impact of New Water Vapor Spectroscopy on Satellite Retrievals.- Spectroscopic and Thermochemical Information on the O2-O2 Collisional Complex Inferred From Atmospheric UV/Visible O4 Absorption Band Profile Measurements.