The vibrational spectrum of an intermediate, T5.12, in the photoreaction of an artificial bacteriorhodopsin (BR) pigment containing a five-membered carbon ring spanning the C-12-C-13=C-14 bonds (BR5.12) is measured by picosecond time-resolved coherent anti-Stakes Raman spectroscopy (PTR/CARS). Observed initially by picosecond transient absorption (PTA) measurements, T5.12 is the only intermediate in the BR5.12 photoreaction (i.e., T5.12 decays only to BR5.12). BR5.12 does not have a photocycle analogous to that in native BR, presumably because the five-membered ring blocks the reaction coordinate leading to C-13=C-14 bond isomerization. Since T5.12 may therefore represent the molecular events (reaction coordinates) that precede C-13=C-14 bond isomerization, its vibrational spectrum may aid in elucidating the primary reaction coordinate(s) in the BR photocycle. Although T5.12 is identified via a red-shifted absorption (660 nm maximum. <3 ps formation with 3 ps BR5.12 excitation and decay in 17 +/- 1 ps), no spectroscopic data which directly characterize the retinal structure in T5.12. and thereby the role of bonding changes, have been available. The PTR/CARS vibrational data presented here show that T5.12 contains (i) an all-trans retinal configuration, (ii) significant hydrogen out-of-plane motion localized in specific normal modes, (iii) increased pi-electron density in the C=C stretching modes manifested by frequency increases, (iv) restricted in-plane C-CH3 rocking motion, and (v) a Schiff-base environment similar to that in BR5.12. These PTR/CARS data also confirm that T5.12 decays exclusively to BR5.12. The vibrational spectrum of T5.12 makes it evident that no complete C=C isomerization nor C-C rotation in any retinal bond occurs upon excitation of BR5.12. The excellent agreement between the kinetic lifetime of T5.12 (from PTA and PTR/CARS data) and its stimulated emission Lifetime suggests that T5.12 may be an excited electronic state. In such a case, the PTR/CARS data presented here are the first to be reported from an excited electronic state of a protein. Regardless of whether T5.12 is an excited or ground electronic state, the vibrational spectra of T5.12 reflect the retinal structure(s) that precedes C-13=C-14 bond isomerization in the BR photocycle. The relevance of T5.12 PTR/CARS data to the native BR photocycle is discussed in terms of the intermediates K-590, J-625, and I-460. Direct analyses of the respective vibrational spectra of T5.12 and K-590 demonstrate that they contain distinctly different retinal structures, but since no vibrational data assignable directly to either I-460 or J-625 have been reported, comparisons of T5.12 with these intermediates are based only on analogy. Comparisons of the vibrational spectra of T5.12 and native BR intermediates independently provide insight into the structural changes in retinal that could occur prior to C-13=C-14 bond isomerization in native BR.