  The present work deals with the formal description of the response to
neutrons of heteronuclear diatomic liquids, with special interest in the case
of hydrogen deuteride as a possible candidate for the moderation process
required in the production of cold neutrons. Preliminary evaluations of the
model giving the neutron double differential cross section of a heteronuclear
vibrating rotor are performed by using, as a first approximation, the ideal gas
law for the centre-of-mass translational dynamics, which is expected to be
appropriate at incident neutron energies above the thermal region. The
unavailability of double differential cross section experimental data on liquid
HD compels to test the model calculations only at an integral level, i.e.
against the only measurement carried out on liquid HD for the determination of
its neutron total cross section. The present findings indicate the evident need
of more accurate measurements of the total cross section, as well as of future
work devoted to double differential cross section determinations and
appropriate simulations of the translational dynamics of this weakly quantum
fluid.
