  We consider tunnel ionization of an atom or molecule in a strong field within
an analytical treatment of the R-matrix method, in which an imaginary boundary
is set up inside the classically forbidden region that acts as a source of
ionized electrons. These electrons are then propagated in the semiclassical
approximation, and relying on a numerical solution of the inner region, which
is accessible using quantum chemical techniques, we describe the subsequent
evolution of the ionized electron and the ionic core.
  Importantly, we show that correlation interactions between the ionized
electrons and those left behind in the core can play a role during ionization,
and that interactions can occur while the electron is still inside the
classically forbidden region that enable tunnelling from channels normally
subject to far greater exponential suppression since they are subject to higher
and wider tunnelling barriers.
  This interaction can be described analytically using saddle-point methods
that find the dominant contributions to the temporal, spatial and momentum
integrals that make up the expressions for the ionization yield. However, these
methods yield results for the angular distributions of the ionized electron
that do not necessarily match experiment and which yield physically
unsatisfactory solutions.
  In this report we develop a formalism to evaluate these integrals exactly,
which yields more precise calculations of the angular distributions while at
the same time providing the language, in terms of exchange of angular momentum,
with which to understand their origins and their differences from previous
cases, thus giving an insight into the fundamental physics of the correlation
interaction process.
