The (3)A(2)(npi*) --> X(1)A(1) phosphorescence excitation spectrum of jet-cooled 4H-pyran-4-thione (PT) was investigated in the region of the (1)A(1) (pipi*) <-- X(1)A(1) absorption band between 27 300 and 28 800 cm(-1). The spectrum exhibits complex features, which are typical for the (strong) vibronic coupling case of two adjacent electronic states. The observed intermediate level structure was attributed to the coupling with a lower lying dark electronic state B-1(1) (npi(2)*), whose origin was estimated to be similar to825-1025 cm(-1) below the origin (1)A(1) (pipi*)(0), using calculations of vibronic state densities in combination with symmetry considerations. Consequences of the vibronic coupling on the decay dynamics of (1)A(1) (pipi*) as well as tentative assignments of vibronic transitions (1)A(1)(pipi*)(v), <-- X(1)A(1) are also briefly discussed. (C) 2002 Elsevier Science B.V. All rights reserved.The (3)A(2)(npi*) --> X(1)A(1) phosphorescence excitation spectrum of jet-cooled 4H-pyran-4-thione (PT) was investigated in the region of the (1)A(1) (pipi*) <-- X(1)A(1) absorption band between 27 300 and 28 800 cm(-1). The spectrum exhibits complex features, which are typical for the (strong) vibronic coupling case of two adjacent electronic states. The observed intermediate level structure was attributed to the coupling with a lower lying dark electronic state B-1(1) (npi(2)*), whose origin was estimated to be similar to825-1025 cm(-1) below the origin (1)A(1) (pipi*)(0), using calculations of vibronic state densities in combination with symmetry considerations. Consequences of the vibronic coupling on the decay dynamics of (1)A(1) (pipi*) as well as tentative assignments of vibronic transitions (1)A(1)(pipi*)(v), <-- X(1)A(1) are also briefly discussed. (C) 2002 Elsevier Science B.V. All rights reserved.