Optical Selection of Rotational and Parity-Resolved States for Rotationally Inelastic Scattering: NO(X(2)Π(1/2), v = 1, j = 1.5e) with Ar and CH(4).

We present new experimental measurements of rotationally inelastic scattering of vibrationally excited NO(XΠ) with Ar and CH. A molecular beam of NO was prepared in a single rotational and parity-resolved state, = 1.5 , in the = 1 vibrational level using mid-infrared radiation from a distributed feedback quantum cascade laser. Following collision with a crossed molecular beam of Ar or CH, rotationally excited NOX, = 1 in the isolated final rotational states = 4.5 and = 10.5 was detected by 1 + 1' resonance-enhanced multiphoton ionization coupled with velocity-map imaging. Differential cross sections and rotational angular momentum polarization moments for inelastic scattering with Ar are in excellent, near-quantitative agreement with quantum scattering predictions on a literature potential energy surface. Images for scattering from CH for both final states show clear evidence of significant rotational excitation in the CH. Overall, a negative correlation is observed in the NO-CH rotational excitation, with higher average CH rotational energy for final NO ' = 4.5 than for = 10.5. For NO = 10.5, higher rotational energies of CH are surprisingly correlated with forward hemisphere scattering, while lower CH rotation is correlated with backward hemisphere scattering. These measurements demonstrate the importance of the preparation of an initial rotational and parity-selected state, and the varied and surprising dynamics that remain underexplored in molecule-molecule inelastic scattering.