Hyperfine quantum beat spectroscopy has been combined with an effective Hamiltonian approach to determine the hyperfine structure of NO(A,v). NO(A,v=0,N=1–7,9J=1.5–8.5,F=0.5–8.5) was produced by pulsed dye laser excitation on the 0–0 band of the NO A2Σ+←X2Π transition at wavelengths around 226nm. The observed line frequencies, along with those reported in previous measurements of NO(A,v=0,3) have been fitted using a non-linear least-squares program with numerical diagonalization of the Hamiltonian matrix. This enabled us to determine the best obtainable sets of hyperfine parameters for the molecule. The vibrational dependence of the hyperfine parameters is discussed in the light of previous experimental and theoretical work on related systems.

Zeeman and hyperfine quantum beat spectroscopies have been used to measure the total elastic plus inelastic angular momentum depolarization rate constants at 300 K for NO(A Σ2+) in the presence of He and Ar. In the case of Zeeman quantum beats it is shown how the applied magnetic field can be used to allow measurement of depolarization rates for both angular momentum orientation and alignment. For the systems studied here, collisional loss of alignment is more efficient than loss of orientation. In the case of NO(A) with He, and to a lesser extent NO(A) with Ar, collisional depolarization is found to be a relatively minor process compared to rotational energy transfer, reflecting the very weak long-range forces in these systems. Detailed comparisons are made with quantum mechanical and quasiclassical trajectory calculations performed on recently developed potential energy surfaces. For both systems, the agreement between the calculated depolarization cross sections and the present measurements is found to be very good, suggesting that it is reasonable to consider the NO(A) bond as frozen during these angular momentum transferring collisions. A combination of kinematic effects and differences in the potential energy surfaces are shown to be responsible for the differences observed in depolarization cross section with He and Ar as a collider.