Potential energy surface vibrational spectroscopy/photodissociation

Vibrationally mediated photodissociation (VMP) can be used to measure the vibrational spectra of small ions, such as V (OCO). Vibrationally mediated photodissociation is a double resonance technique in which a molecule first absorbs an IR photon. Vibrationally excited molecules are then selectively photodissociated following absorption of a second photon in the UV or visible [114—120]. With neutral molecules, VMP experiments are usually used to measure the spectroscopy of regions of the excited-state potential energy surface that are not Franck-Condon accessible from the ground state and to see how different vibrations affect the photodissociation dynamics. In order for VMP to work, there must be some wavelength at which vibrationally excited molecules have an electronic transition and photodissociate, while vibrationally unexcited molecules do not. In practice, this means that the ion has to have a... 

Figure 5.9 Schematic potential energy surfaces for two-color vibrationally mediated photodissociation spectroscopy. The location of the initial excitation on the upper repulsive surface is varied by the choice of the intermediate vibrational energy. Taken with permission from Likar et al. (1988).

Abstract In the present study, the effect of the potential energy surface representation on the infrared spectra features of the and Df clusters is investigated. For the spectral simulations, we adopted a recently proposed (Sanz-Sanz et al. in Phys Rev A 84 060502-1-4, 2011) two-dimensional adiabatic quantum model to describe the proton-transfer motion between the two H2 or D2 units. The reported calculations make use of a reliable on the fly DFT-based potential surface and the corresponding new dipole moment surface. The results of the vibrational predissociation dynamics are compared with earlier and recent experimental data available from mass-selected photodissociation spectroscopy, as well as with previous theoretical calculations based on an analytical ab initio parameterized surfaces. The role of the potential topology on the spectral features is studied, and general trends are discussed. 

Molecular electronic absorption and emission spectroscopy, photodissociation, Raman spectroscopy, and vibrational overtone spectroscopy have been examined from a time-dependent perspective for their implications for potential energy surfaces and dynamics. A semiclassical point of view greatly aids intuitive understanding and computation of these various spectroscopies from limited local and regional knowledge of the potential surface. 

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