Formation of NO(j′=7.5) molecules with sub-kelvin translational energy via molecular beam collisions with argon using the technique of molecular cooling by inelastic collisional energy-transfer

We report the cooling of nitric oxide molecules in a single collision between an argon atom and an NO molecule at collision energies of 5.65+/-0.36 kJ/mol and 14.7+/-0.9 kJ/mol in a crossed molecular beam apparatus. We have produced in significant numbers (similar to10(8) molecules cm(-3) per quantum state) translationally cold NO((2)Pi(1/2), v'=0, j'=7.5) molecules in a specific quantum state with an upper-limit laboratory-frame rms velocity of 14.8+/-1.1 m/s, corresponding to a temperature of 406+/-28 mK. The translational cooling results from the kinematic collapse of the velocity distribution of the NO molecules after collision. Increasing the collision energy by increasing the velocity of the argon atoms; as we do here, does shift the scattering angle at which the cold molecules appear, but does not result in an experimentally measurable change in the velocity spread of the cold NO. This is entirely consistent with our analysis of the kinematics of the scattering which predicts that the velocity spread will actually decrease with increasing argon atom velocity.