The simulated photoelectron spectrum of 1-propynide

摘要

The negative ion photoelectron spectrum of 1-propynide is computed by employing the multimodevibronic coupling approach. A three-state quasidiabatic Hamiltonian, Hd, is reported, whichaccurately represents the ab initio determined equilibrium geometries and harmonic frequencies ofthe ground X 2A1 state as well as the low-lying Jahn–Teller distorted components of the A 2E excitedstate. It also reproduces both the minimum energy crossing point (MECP) on the symmetry-required2Ex-2Ey conical intersection seam and the MECP on the same symmetry 2A1-2Ex conical intersectionseam. Hd includes all terms through second order in internal coordinates for both the diagonal andoff-diagonal blocks. It is centered at the 2Ex-2Ey MECP and is determined using ab initio gradientsand derivative couplings near both the 2E,-2Ey MECP and the X 2A1 equilibrium geometry. Thisconstruction is enabled by a recently reported normal equation based algorithm. The C3,, symmetryof the system is used to significantly reduce the computational cost of the ab initio treatment. ThisHd is then expressed in a vibronic basis that is chosen for its ability to reduce the dimension of thevibronic expansion. The vibronic Hamiltonian matrix is diagonalized to obtain a negative ionphotoelectron spectrum for 1-propynide-h3. The determined spectrum compares favorably withprevious spectroscopic results. In particular, the lines attributable to the 2E state are found to bemuch weaker than those corresponding to the 2A1 state of 1-propynyl. This diminution of the 2Estate is attributable principally to the 2Ex-2A1 conical intersection rather than an intrinsically smallelectronic transition moment for the production of the 2E state.