Molecular level crossing and the geometric phase effect from the optical Hanle perspective

Abstract

Level-crossing spectroscopy involves lifting the degeneracy of an excited state and using the interference of two nearly degenerate levels to measure the excited state lifetime. Here we use the idea of interference between different pathways to study the momentum-dependent wave packet lifetime due an excited state level-crossing (conical intersection) in a molecule. Changes in population from the wave packet propagation are reflected in the detected fluorescence. We use a chirped pulse to control the wave packet momentum. Changing the chirp rate affects the transition to the lower state through the conical intersection. It also affects the interference of different pathways in the upper electronic state, due to the geometric phase acquired. Increasing the chirp rate decreases the coherence of the wave packet in the upper electronic state. This suggests that there is a finite momentum dependent lifetime of the wave packet through the level-crossing as function of chirp. We dub this lifetime the wave packet momentum lifetime. : 33.15.Hp, 32.50.+d, 33.80.Be, 78.20.Bh, 42.65.Re ( b ). When both levels are nearly degenerate and excited simultaneously, the fluorescence is proportional to   2 ab AA  . Resonance occurs when the magnetic field is zero and increasing the magnetic field strength partially destroys the coherence. Thus, the absolute radiative lifetime can be measured by detecting the fluorescence as a function magnetic field strength, without any knowledge of the density of the emitters [13]. Electronic level-crossings (conical intersections) occur in nearly all molecules and are responsible for many excitedstate chemical processes [2][3][4][14][15][16]. The isomerization PACS

Electron vacancy-level dependent hybrid photoionization of the F−@ C60+ molecule: a novel effect

“…A maximum entanglement between nuclear and electron spins is predicted for atoms at avoided crossings demonstrating a relation between the level crossings and Berry phases at the level of the Breit-Rabi Hamiltonian [29]. Recently, the effect of chirped laser-pulse control in the interference between different pathways to study the momentum-dependent wave-packet using molecular levelcrossing spectroscopy is studied [30]. Experimentally, a very efficient transfer through molecular bound states is shown by magnetically tuned mixing of two neighboring molecular levels [31]; this activated forbidden radio-transitions.…”