RESONANTLY ENHANCED MULTIPHOTON IONIZATION OF N2 A''1-SIGMA-G+ (UPSILON' = UPSILON'') [- X1-SIGMA-G+ (UPSILON'' = 0, 1, 2) .2. ALIGNMENT AND ORIENTATION MEASUREMENTS

The N2 a"(1)SIGMA(g)+ <-- X(1)SIGMA(g)+ (0,0) 2 + 1 resonance-enhanced multiphoton ionization (REMPI) transition has been used to measure angular momentum alignment and orientation of N2 scattered from Ag(111). This two-photon SIGMA <-- SIGMA transition has been used for the first time to measure angular momentum alignment and orientation moments. Alignment of N2 molecules has been measured using the O, Q, and S branches, and orientation has been measured using the O and S branches. For the alignment measurements employing excitation of the Q branch by linearly polarized light, the effects of optical ellipticity and polarization saturation have been investigated as well as the sensitivity of the calculated alignment to our estimate of the character of the virtual state in the N2 a"(1)SIGMA(g)+ <-- X(1)SIGMA(g)+ (0,0) transition. For the orientation measurements, two different techniques were employed and compared. In the first technique, the optical ellipticity is varied while the major axis of polarization is fixed in space. In the second technique, the optical ellipticity and the direction of the major axis of ellipticity are simultaneously varied. The S and O branches are highly sensitive to alignment and orientation, yielding excellent values for A0+{2} and A1-{1} but less accurate values for A0+{4} and A1-{3}. The Q branch, though less sensitive than the O and S branches, yields good qualitative values for the A0+{2} alignment moment in the limit of very small optical ellipticity and near-zero saturation.