Polyatomic molecules probe techniques

As discussed in Section II, the excited-state dynamics of polyatomic molecules is dictated by the coupled flow of both charge and energy within the molecule. As such, a probe technique that is sensitive to both nuclear (vibrational) and electronic configuration is required in order to elucidate the mechanisms of such processes. Photoelectron spectroscopy provides such a technique,... 

The most powerful technique for studying VER in polyatomic molecules is the IR-Raman method. Initial IR-Raman studies of a few systems appeared more than 20 years ago [16], but reeently the teehnique has taken on new life with newer ultrafast lasers such as Ti sapphire [39]. With more sensitive IR-Raman systems based on these lasers, it has become possible to monitor VER by probing virtually every vibration of a polyatomic molecule, as illustrated by recent studies of chloroform [40], acetonitrile [41. 42] (see example C3.5.6.6 below) and nitromethane [39, 43]. 

The solvation shells of ions may not be spherically symmetrical, a phenomenon that occurs at the surfaces of solutions. The solvent molecules may then polarize the ions, even if they are monatomic, and thus affect their properties. However, in the bulk of the solutions, monatomic ions reside in a spherically symmetrical field and are themselves little affected by the solvent. This is not necessarily the case for polyatomic ions, even for those that have a globular shape. This effect is most noted in the vibrational and rotational relaxation times of polyatomic ions. The relaxation is measurable by the pump/probe technique, where the laser beam at the wave-number of the ground state is followed after a short interval by a probe beam at the level of the excited state, following its exponential decay. 

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