Dynamics Of Polyatomic Molecules Research Articles

Theoretical studies on the femtosecond real-time measurement of ultrafast electronic decay in polyatomic molecules

We present a computer simulation of the real-time detection of ultrafast electronic decay dynamics in polyatomic molecules with femtosecond laser pulses. The intramolecular non-Born-Oppenheimer quantum dynamics is treated numerically exactly for a two-state three-mode vibronic coupling model representing the conically intersecting S1 and S2 excited states of pyrazine. The pump–probe signal is evaluated in lowest order perturbation theory with respect to the radiation–matter interaction by numerical integration over the pump and probe pulses. We discuss in some detail the dependence of the pump–probe signal on the properties of the laser pulses (frequencies and pulse durations). The calculations predict a dramatic (∼12 000 cm−1) and ultrafast (∼20 fs) red shift of the stimulated-emission signal as well as distinctive quantum beats in the pump–probe signal as a function of the delay time. Both effects are very pronounced and should therefore be relatively easily detectable experimentally. They are expected to be generic features of ultrafast internal-conversion processes in polyatomic molecules.

Spectroscopy and excited state dynamics of polyatomic molecules in supersonic beams

The fundamental aspects of excited dynamics in polyatomic molecules contains many effects, which while understood in the limit of a sparse density of states in a simple diatomic, have long eluded study. With a combination of lasers, supersonic beams to prepare ultra-cold molecules and novel types of spectroscopic approaches, one can begin to observe the dynamics and properties of superposition states which are the basis of phenomena ranging from autoionization, to predissociation, to quantum interference effects and intramolecular vibrational redistribution. This paper will review selected studies on large polyatomic molecules and their clusters.

Picosecond infrared multiphoton ionization of chromyl chloride

Picosecond infrared multiphoton ionization (MPI) was demonstrated as a viable technique for monitoring the population in the excited states in a polyatomic molecule such as CrO 2Cl 2. This method differs from resonant MPI in the sense that tunable UV laser is not needed. By time delaying the excitation laser pulse and the ionization laser pulse, dynamical information on energy relaxation of the excited state can be obtained in the usual manner. This technique was demonstrated with CrO 2Cl 2 with 532 nm excitation. It was observed that at this frequency the relaxation was due mainly to collisional deactivation, in agreement with previous studies. This technique should be applicable to the investigation of ultrafast collisionless intramolecular dynamics in polyatomic molecules.

Applications of a simple dynamical model to the reaction path Hamiltonian: tunneling corrections to rate constants, product state distributions, line widths of local mode overtones, and mode specificity in unimolecular decomposition

A simple, but often reasonably accurate dynamical model - a synthesis of the semiclassical perturbtion (SCP) approximation of Miller and Smith and the infinite order sudden (IOS) approximation - has been shown previously to take an exceptionally simple form when applied to the reaction path Hamiltonian derived by Miller, Handy, and Adams. This paper shows how this combined SCP-IOS reaction path model can be used to provide a simple but comprehensive description of a variety of phenomena in the dynamics of polyatomic molecules.

State-to-state photochemical reaction dynamics in polyatomic molecules

The generalized Franck–Condon theory of the dissociation of linear triatomic molecules is presented, including proper descriptions of the bending and rotational motions on the bound and unbound electronic potential energy surfaces. The role of angular momentum conservation is made explicit through analytical expressions for rotational and orbital angular momentum distributions of the photofragments. The theory is also applied to the calculation of photofragment angular distributions and preliminary results are described.