A crossed-beam experiment on intramultiplet mixing collisions with short-lived Ne** {(2p)5(3p)} atoms

We describe the design, operation, and calibration of a crossed-beam experiment for the study of intramultiplet mixing collisions of short-lived electronically excited Ne{(2p)5(3p)}≡{α} atoms with ground-state atoms/molecules. The excellent performance of almost 1 kHz/Å2 (number of counts per unit of inelastic cross section) enables us to measure, with good accuracy, absolute total Ne**-X cross sections Q‖Mk‖l←k, for the {α}k→{α}l transition. Here Mk is the magnetic quantum number of the electronic angular momentum J of the initial {α}k state with respect to the asymptotic relative velocity. The polarized {α}k state is produced with a polarized laser. Narrow-band interference filters are used to detect the fluorescence radiation from the short-lived {α}k and {α}l states. An extensive series of measurements has been undertaken to calibrate the experiment. These are related to, e.g., beam properties, the optical-pumping process, and the optical detection system. The basic principles of the collision experiment itself have been thoroughly examined as well. We discuss the kinds of experiments it is possible to perform. These have yielded absolute (within 30%) cross sections between 0.05 and 50 Å2. Very strong polarization effects have been observed, with 0.1≲Q‖0‖l←k/Q‖1‖l←k ≲10. The average collision energy has been varied between 50 and 250 meV (depending to some extent on the collision partner), by using a seeded primary beam and by manipulating the Newton diagram of primary- and secondary-beam velocity vectors. Time-of-flight measurements with a laser chopper have been performed as well. The wide range of Ne**-collision partners offers the option of studying intramultiplet mixing pure (He, Ne), and in conjunction with Penning ionization (noble gas atoms Ar, Kr, Xe) or even angular-momentum coupling and anisotropy effects (molecules, from H2 to CO2, N2O)