https://doi.org/10.1007/s100530070110
The internal energy of small ammonia clusters in a supersonic beam and after scattering off LiF(100)
Physikalisches Institut, Westfälische Wilhelms-Universität,
48149 Münster, Germany
Received:
18
October
1999
Revised:
10
December
1999
Published online: 15 July 2000
The photoionization efficiency (PIE) of neutral ammonia clusters is
studied as a function of photon energy. From these curves the internal
energies of clusters in the incident supersonic beam and of clusters
surviving after scattering off a LiF(100) surface are derived. A
supersonic expansion of ammonia seeded in He produces small clusters
of various size but with uniform kinetic energy of about 285 meV per
monomer molecule. The mass distribution of clusters in the jet and of
the scattered particles is measured in a reflecting time-of-flight
mass spectrometer by single photon photoionization using vacuum
ultraviolet (VUV) laser radiation tunable between 
and 
. In the incident beam the internal energies
of clusters up to n = 15 do not vary significantly and amount to
an average of about 
. After scattering off LiF(100)
the internal energy of clusters up to n = 4 increases with fragment size
and amounts to about half a monomer binding energy.
PACS: 36.40.Sx – Diffusion and dynamics of clusters / 68.45.Da – Adsorption and desorption kinetics; evaporation and condensation / 82.65.Pa – Surface-enhanced molecular states and other gas-surface interactions
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000
