  This paper reports an implementation of Hartree-Fock linear response with
complex orbitals for computing electronic spectra of molecules in a strong
external magnetic fields. The implementation is completely general, allowing
for spin-restricted, spin-unrestricted, and general two-component reference
states. The method is applied to small molecules placed in strong uniform and
non-uniform magnetic fields of astrochemical importance at the Random Phase
Approximation level of theory. For uniform fields, where comparison is
possible, the spectra are found to be qualitatively similar to those recently
obtained with equation of motion coupled cluster theory. We also study the
behaviour of spin-forbidden excitations with progressive loss of spin symmetry
induced by non-uniform magnetic fields. Finally, the equivalence of length and
velocity gauges for oscillator strengths when using complex orbitals is
investigated and found to hold numerically.
