SRI INTERNATIONAL PROPOSES A LABORATORY STUDY AIMED AT IMPROVING THE RELIABILITY OF NON-LOCAL THERMODYNAMIC EQUILIBRIUM (NON-LTE) MODELS FOR RETRIEVAL OF WATER VAPOR NUMBER DENSITY PROFILES IN THE EARTH'S MESOSPHERE AND LOWER THERMOSPHERE (MLT) REGIONS. IN THE CURRENT NON-LTE MODELS THE COLLISIONAL PROCESS THAT PRESENTS THE LARGEST SOURCE OF UNCERTAINTY IS THE VIBRATION-TO-VIBRATION (V-V) ENERGY EXCHANGE BETWEEN H2O(010) AND O2(1). IN THE PROPOSED PROJECT THE RATE COEFFICIENT FOR THIS PROCESS WILL BE DETERMINED AS A FUNCTION OF TEMPERATURE INCLUDING LOW TEMPERATURES RELEVANT TO THE MLT REGION. THE PUBLISHED ESTIMATES OF THIS RATE COEFFICIENT SPAN ALMOST AN ORDER OF MAGNITUDE AND THE EXPERIMENTS AT AND ABOVE ROOM TEMPERATURE YIELDED A VALUE 2-3 TIMES LOWER THAN THE VALUES TYPICALLY DERIVED BY MODELING THE INFRARED EMISSIONS FROM H2O(010). LOW-TEMPERATURE LABORATORY MEASUREMENTS ARE ESSENTIAL TO CONSTRAIN THE MODELS AND ENABLE RELIABLE WATER DENSITY RETRIEVAL FROM MEASURED INFRARED EMISSIONS. THE PROPOSED EXPERIMENTS WILL EMPLOY A STATE-SELECTIVE TWO-LASER APPROACH. VIBRATIONALLY EXCITED POPULATIONS OF THE TWO SPECIES WILL BE PRODUCED USING STIMULATED RAMAN SCATTERING (SRS) OR OZONE PHOTOLYSIS. THE KINETICS OF THE V-V TRANSFER WILL BE INVESTIGATED VIA RESONANCE-ENHANCED MULTIPHOTON IONIZATION (REMPI) DETECTION OF H2O(010) AND O2(1) INFRARED ABSORPTION OR EMISSION. THE RATE COEFFICIENT WILL BE MEASURED IN THE 220-300 K TEMPERATURE RANGE PROVIDING DATA THAT WILL ENABLE A RELIABLE EXTRAPOLATION TO EVEN LOWER TEMPERATURES. THE RESULTS OF THIS INVESTIGATION WILL HAVE A CRUCIAL POSITIVE IMPACT ON THE QUANTITATIVE EXTRACTION OF THE WATER VAPOR ALTITUDE PROFILES FROM THE 6.3 MICROMETER EMISSION CHANNEL OF THE SOUNDING OF THE ATMOSPHERE USING BROADBAND EMISSION RADIOMETRY (SABER) INSTRUMENT ABOARD THE THERMOSPHERE-IONOSPHERE-MESOSPHERE ENERGETICS AND DYNAMICS (TIMED) SATELLITE.