We report direct measurements of the statehyphen;tohyphen;state rotational energy transfer rates for N2(ugr;=1) at 298 K. Stimulated Raman pumping ofQhyphen;branch (ugr;=1larr;0) transitions is used to prepare a selected rotational state of N2in the ugr;=1 state. After allowing an appropriate time interval for collisions to occur, 2+2 resonancehyphen;enhanced multiphoton ionization is used (through theathinsp;1Pgr;glarr;Xthinsp;1Sgr;+gtransition) to detect the relative population of the pumped level and other levels to which rotational energy transfer has occurred. We have performed a series of measurements in which a single even rotational level (Ji=0ndash;14) is excited and the timehyphen;dependent level populations are recorded at three or more delay times. This data set is then globally fit to determine the best set of statehyphen;tohyphen;state rate constants. The fitting procedure does not place any constraints (such as an exponential gap law) on theJor energy dependence of the rates. We compare our measurements and besthyphen;fit rates with results predicted from phenomenological rate models and from a semiclassical scattering calculation of Koszykowskietal. lsqb;J. Phys. Chem.91, 41 (1987)rsqb;. Excellent agreement is obtained with two of the models and with the scattering calculation. We also test the validity of the energyhyphen;corrected sudden (ECS) scaling theory for N2by using our experimental transfer rates as basis rates (J=Lrarr;0), finding that the ECS scaling expressions accurately predict the remaining rates.
展开▼
