Emission spectra obtained from bulk-gas methinophosphide (HCP) have been interpreted by means of a Lie algebraic theory that describes explicit non-rigidity of the molecular framework. Fluorescence accompanying selective excitation of A ¹A″- X ¹Σ⁺ vibronic bands was dispersed under moderate resolution, with substantial activity of the ν₂ H-C-P bending mode reflecting the bent-from-linear nature of the A ← X transition. Aside from furnishing an economical parameterization for energy level patterns, the algebraic treatment permits Franck-Condon intensities to be evaluated quantitatively. The equilibrium structure deduced for the A ¹A″ state is in good accord with quantum chemistry calculations except for substantially less than predicted elongation of the C-P bond upon electronic promotion.