Laser probing of the rotational alignment of N + 2 drifted in helium

Results are presented on laser-induced fluorescence studies of the rotational alignment of N⁺₂ drifted in helium. The alignment which is caused by collisions of the ions with the helium buffer gas is observed in the uniform electric field of a drift tube. The angular momentum vectors of the ions are preferentially aligned perpendicular to the electric field vector. At a drift field of 14 Td, corresponding to a collision energy of 52 meV (c.m.), a quadrupole moment A⁽²⁾₀=-0.11±0.03 is determined for the N=10 rotational state. This yields an approximate population ratio of 2:3 for finding molecules with rotational angular momentum vectors parallel and perpendicular to the electric field vector, respectively. In addition to the alignment studies, a detailed characterization of the drift tube using laser-induced fluorescence detection of N⁺₂ is presented. Theoretical results for the determination of alignment parameters using saturated laser-induced fluorescence are presented.