Communication: Direct angle-resolved measurements of collision dynamics with electronically excited molecules: NO(A²Σ⁺)+ Ar

We report direct doubly differential (quantum state and angle-resolved) scattering measurements involving short-lived electronically excited molecules using crossed molecular beams. In our experiment, supersonic beams of nitric oxide and argon atoms collide at 90. In the crossing region, NO molecules are excited to the A²S⁺state by a pulsed nanosecond laser, undergo rotationally inelastic collisions with Ar atoms, and are then detected 400 ns later (approximately twice the radiative lifetime of the A ²S⁺state) by 1 1' multiphoton ionization via the E²S⁺ state. The velocity distributions of the scattered molecules are recorded using velocity-mapped ion imaging. The resulting images provide a direct measurement of the state-to-state differential scattering cross sections. These results demonstrate that sufficient scattering events occur during the short lifetimes typical of molecular excited states (~200 ns, in this case) to allow spectroscopically detected quantum-state-resolved measurements of products of excited-state collisions. © 2011 American Institute of Physics.