  In a previous work [Phys. Rev. A \textbf{66}, 0134XX (2002)] we noted a
partial disagreement between quantum R-matrix and semiclassical calculations of
photoabsorption spectra of molecules in a magnetic field. We show this
disagreement is due to a non-vanishing contribution of processes which are
forbidden according to the usual semiclassical formalism. Formulas to include
these processes are obtained by using a refined stationary phase approximation.
The resulting higher order in $\hbar$ contributions also account for previously
unexplained ``recurrences without closed-orbits''. Quantum and semiclassical
photoabsorption spectra for Rydberg atoms and molecules in a magnetic field are
calculated and compared to assess the validity of the first-order forbidden
orbit contributions.
