The T-1(n,pi*) <- S-0 transition of 2-cyclopenten-1-one (2CP) was investigated by using phosphorescence excitation ( PE) spectroscopy in a free-jet expansion. The origin band, near 385 nm, is the most intense feature in the T-1(n,pi*) <- S-0 PE spectrum. A short progression in the ring-bending mode ( nu'(30)) is also observed. The effective vibrational temperature in the jet is estimated at 50 K. The spectral simplification arising from jet cooling helps confirm assignments made previously in the room-temperature cavity ringdown (CRD) absorption spectrum, which is congested by vibrational hot bands. In addition to the origin and nu'(30) assignments, the jet-cooled PE spectrum also confirms the 28(0)(1) (C=O out-of-plane wag), 29(0)(1) (C=C twist), and 19(0)(1) (C=O in-plane wag) band assignments that were made in the T-1(n,pi*) <- S-0 room-temperature CRD spectrum. The temporal decay of the T-1 state of 2CP was investigated as a function of vibronic excitation. Phosphorescence from the nu' = 0 level persists the entire time the molecules traverse the emission detection zone. Thus the phosphorescence lifetime of the nu' = 0 level is significantly longer than the 2 mu s transit time through the viewing zone. Higher vibrational levels in the T-1 state have shorter phosphorescence lifetimes, on the order of 2 mu s or less. The concomitant reduction in emission quantum yield causes the higher vibronic bands ( above 200 cm(-1)) in the PE spectrum to be weak. It is proposed that intersystem crossing to highly vibrationally excited levels of the ground state is responsible for the faster decay and diminished quantum yield. The jet cooling affords partial rotational resolution in the T-1( n, pi*) <-S-0 spectrum of 2CP. The rotational structure of the origin band was simulated by using inertial constants available from a previously reported density functional ( DFT) calculation of the T-1(n,pi*) state, along with spin constants obtained via a fitting procedure. Intensity parameters were also systematically varied. The optimized intensity factors support a model that identifies the S-2(pi,pi*) <- S-0 transition in 2CP as the sole source of oscillator strength for the T-1(n,pi*) <- S-0 transition.