IONIZATION OF AMMONIA MOLECULES BY COLLISION WITH METASTABLE NEON ATOMS 


M.Ben Arfa$^\ast$, B.Brunetti$^\sharp$, P.Candori$^\sharp$,
M.Cherid$^\ast$, S.Falcinelli$^\circ$, B.Lescop$^\ast$,
D.Malfatti$^\sharp$, F.Vecchiocattivi$^\circ$


$^\ast$Laboratoire de Physique des Collisions -Faculte' des Sciences,
Universite' des Brest, 29285 Brest, France
$^\sharp$Dipartimento di Chimica - Universita' di Perugia, 06123
Perugia, Italy
$^\circ$Istituto Tecnologie Chimiche, Facolta' di Ingegneria, 06123
Perugia, Italy


The ionization of ammonia by collision with metastable neon atoms has
been studied by measuring the energy spectrum of emitted electrons and
the mass spectrum of product ions. Nascent NH$_3^+$ ions are formed in
the ground, X$^2$A', and in the first excited, A$^2$E, state. The latter
then gives rise to NH$_2^+$ fragments. Total ionization cross sections
and branching fractions, NH$_2^+$/NH$_3^+$, have been measured as a
function of collision energy in the 0.03-0.2 eV energy range . At higher
collision energy the NH&_2^+$/NH$_3^+$ ratio increases.