Photoinduzierte Stoßprozesse metastabiler Wasserstoffatome mit H2 im Energiebereich von 0,05 — 0,47 eV

Molecular hydrogen was excited by selective absorption of ultraviolet radiation of appropriate wavelength into the vibrational levels ν′ 3, 4, and 5 of the electronic D (1IIu)-state. For the radiation bandwidth chosen the molecule was only formed in the rotational levels J = 1 and 2 of the R-branch. The excited molecules decay by predissociation into two hydrogen atoms of translational energy which is equal to one half of the difference between the excitation and dissociation energies. One of the atoms is formed in its first excited state. The formation of the excited species can be proven by its fluorescence (Lymanα-radiation). As a result the measurements show, that the excited atoms are all in the metastable 2S-state and not in the short-lived 2P -state. Without electric fields these metastable atom s loose their excitation energy in collisions with the surrounding hydrogen molecules. One part (a) follows an induced transition to the electronic ground state by the emission of Lyα-radiation (1216 Å), the other part (b) is transformed to products or undergoes an energy transfer process without emitting Lyα-radiation. If a quenching field is applied spontaneous emission will compete with collisional deactivation, which allows the deactivation cross sections to be calculated. These cross sections are between 50 and 100 Å2 (a) and about 50 Å2 in case (b). In case (a) the collision cross section increases with the velocity of the particles whereas in case (b) a constant value was found.