One of our major goals has been the study of collisions involving molecular ions at low temerature ( ~1 - 30 K). (De Lucia, et al.)
For this work a novel apparatus was
developed to produce large quantities of thermal molecular ions at
temperatures well below the freezing points of their precursor neutrals. The
challenge for our studies was the development of a system which produces an
adequate number density of molecular ions at temperature while simultaneously
allowing the pressure and temperature of the collisional environment to be
controlled and characterized. This was achieved by the
development of a cell
which is based both on the magnetic enhancement of ion production in an abnormal
glow discharge and on collisional cooling. This apparatus has been used to
study the pressure broadening of the J = 3 - 2 rotational transition of
HCO+ in H2 gas at temperatures in the range 11 - 30 K.
The figure compares the results of our experiment with Langevin capture theory.