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) over tilde (1)A" - (X) over tilde (1)Sigma(+) vibronic bands was dispersed under moderate resolution, with substantial activity of the nu(2) H-C-P bending mode reflecting the bent-from-linear nature of the (A) over tilde <-- (X) over tilde 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) over tilde (1)A" state is in good a(c)cord with quantum chemistry calculations except for substantially less than predicted elongation of the C-P bond upon electron promotion. (C) 2002 Elsevier Science B.V. All rights reserved.