State-to-state differential cross sections for spin–multiplet-changing collisions of NO(X 2Π1/2) with argon

Abstract

Rotational state-resolved differential cross sections (DCS) for spin–multiplet-changing collisions of NO (X 2 Π 1/2 →X 2 Π 3/2 ) with Ar are presented and compared to results from previous experimental and theoretical studies performed on the NO/Ar system. A crossed molecular beam apparatus coupled with velocity-mapped ion imaging was used to measure complete (θ=0°–180°) DCS for scattering of NO (X 2 Π 1/2 ,j=0.5) into NO (X 2 Π 3/2 ,j ′ ) rotational states ranging from j ′ =1.5 to j ′ =12.5. Scattered products were detected by state-selective ionization using (1+1′) resonance-enhanced multiphoton ionization via the A 2 Σ + state. State-to-state DCS were extracted in the center-of-mass frame of reference for energy transfer at a center-of-mass collision energy of ∼530 cm−1. Studies performed using horizontally and vertically polarized excitation laser beams yielded DCS which were remarkably similar, indicating that state-to-state scattering for this system is insensitive to probe beam polarization. Experimentally determined angular scattering distributions show primarily forward scattering for low-energy rotational states (j<7.5), with side- and back-scattering increasing with product angular momentum. The scattering results are compared and contrasted to results from earlier experimental investigations and to theoretical results from quantum close-coupling calculations based on ab initio coupled cluster CCSD(T) potential energy surfaces.