Line Shape for Water Vapor and Other Atmospheric Asymmetric Rotor Molecules

University Of Massachusetts Lowell, Lowell MA

Investigators

Abstract

This project involves developing a theoretical framework for calculating spectroscopic parameters (pressure-broadened half-widths and pressure-induced line shifts) for trace gases in the terrestrial atmosphere. Accurate half-widths are needed for interpreting remote sensing data and in line- by-line models used to calculate radiative forcing from greenhouse gases. The inclusion of the line shift in profile retrievals also reduces errors in these retrievals. Data for thousands of ro-vibrational transitions are needed. A theoretical model is needed that is computationally efficient and capable of determining the desired parameters accurately. The complex Robert-Bonamy (CRB) formalism is the basis of the theoretical approach. The calculations use realistic molecular dynamics, all relevant terms in the interaction potential, and no cutoff procedure. The effects of explicit velocity averaging on the half-width and line shift will be studied. The intermolecular potential and the dependence of the half-width and line shift on the parameters describing this potential will be investigated. The potentials will be optimized by nonlinear least-squares fits to experimental and theoretical data. Initial calculations will be done for species for which there are experimental measurements of both parameters for several vibrational bands to compare with, such as water and ozone perturbed by molecular nitrogen and oxygen. The theory will also be extended to consider self-broadening and shifting of these species and other developments of the wavefunctions. The vibrational state, rotational state, and temperature dependence of these collision-induced parameters will be investigated. This work will improve our confidence in spectroscopic remote sensing results and allow a better determination of the radiative forcing of greenhouse gases. Research experiences for undergraduate students will be provided. This award is supported jointly by the Atmospheric Chemistry Program (Division of Atmospheric Sciences/Directorate of Geosciences) and Experimental Physical Chemistry Program (Division of Chemistry/Directorate of Mathematical and Physical Sciences).