Laser-induced fluorescence and dispersed fluorescence spectroscopy of jet-cooled 1-phenylpropargyl radical

The D₁(A² ″) - D₀(A² ″) electronic transition of the resonance-stabilized 1-phenylpropargyl radicalooled discharge of 3-phenyl-1-propyne, has been investigated in detail by laser-induced fluorescence excitation and dispersed single vibronic level fluorescence (SVLF) spectroscopy. The transition is dominated by the origin band at 21 007 cm^-1, with weaker Franck-Condon activity observed in a′ fundamentals and even overtones and combinations of a″ symmetry. Ab initio and density functional theory calculations of the D₀ and D₁ geometries and frequencies were performed to support and guide the experimental assignments throughout. Analysis of SVLF spectra from 16 D ₁ vibronic levels has led to the assignment of 15 fundamental frequencies in the excited state and 19 fundamental frequencies in the ground state; assignments for many more normal modes not probed directly by fluorescence spectroscopy are also suggested. Duschinsky mixing, in which the excited state normal modes are rotated with respect to the ground state modes, is prevalent throughout, in vibrations of both a′ and a″ symmetry.