State-to-State Rate Coefficients for NH(3)–NH(3) Collisions from Pump–Probe Chirped Pulse Experiments

[Image: see text] The kinetics of rotational inelastic NH(3)–NH(3) collisions are recorded using pump–probe experiments, carried out with a K-band waveguide chirped pulse Fourier transform microwave spectrometer, in which the population of one inversion doublet is altered by the pump pulse. Due to self-collisions, the resulting deviation from equilibrium propagates to other states and, thus, can be interrogated by probe pulses as a function of the pump–probe delay time. A clear hierarchy of the state-to-state collision processes is found and subsequently translated into propensity rules. State-to-state rate coefficients are estimated, first via an analysis of the kinetics, and then more robustly and accurately derived from the pressure-dependent measurements using a global fitting procedure.