Experiments on the Production and Extinction of the2sState of the Hydrogen Atom

The rates of production and extinction of the metastable $2s$ state of the hydrogen atom during passage of an initially pure proton beam through molecular hydrogen are studied. Iodine-filled Geiger counters were used to detect the Lyman alpha radiation from the metastable beam component, which was quenched by electric fields for purposes of observation. An observed peak in the growth of the metastable beam component at 15 keV projectile energy leads to a cross section for the extinction of the metastable atom by collision with molecular hydrogen in excess of 10^-15 cm² per target atom. The rate of extinction of the metastable atom by dc electric fields between 50 and 500 V/cm is studied and the weak-field time-independent perturbation-theory treatment of this process is verified. This extinction rate is obtained by observing the decay length of the Lyman alpha radiation emerging from the metastable beam component as a function of electric field. The effective cross section for electron capture into the $2s$ state by 15-keV protons in hydrogen is compared with the best available cross section for the process e+H₂→countableuv, and is estimated to be 1×{}10^-17 cm² per target atom. For the same energy and target, the effective cross section for excitation of $1s$ projectiles to the $2s$ state is estimated to be 1.5×{}10^-18 cm² per target atom.