Research

The idea of performing ground state dissociation of diatomic molecules by vibrational ladder-climbing via chirped pulses has been proposed theoretically for quite sometime now and also been demonstrated in a recent experiment. The chirping of a laser pulse is modulating its instantaneous frequency with time. Attempts to control the dissociation dynamics of a polyatomic molecule using chirped-pulse are foiled by the phenomenon of IVR. IVR is a roadblock to performing mode-specific chemistry. On the other hand, recent studies indicate that molecules undergoing facile IVR can be dynamically stabilized by some special conditions. These conditions are related to the existence of “dynamical traps” or “resonance junctions” involving the intersection of several anharmonic resonances in the molecular phase space. An interesting question to ask is whether appropriate weak laser fields can "guide" the molecules through a sequence of dynamical traps, ultimately leading to the scission of the desired bond. In our group, we are theoretically analyzing the laser-driven dissociation dynamics of the model HCN system. It is a linear molecule having only two degrees of freedom (CH stretch & CN stretch). In our classical mechanical calculations, we are studying how the dissociation probability is getting modulated with varying laser frequency and how this modulation is related to the structures/features of the "Arnold's web" or network of nonlinear resonances.

We have observed that the dissociation probability (of the CH mode) shows oscillatory behavior with varying laser frequency. We have also performed wavelet-based time-frequency analysis to compute local frequencies which allow us to construct Arnold web for our model system. Future studies would be to perform quantum dynamical calculations and show the quantum-classical correspondence for this system. The principle motivation of this project is to connect the oscillation features in dissociation probability with the specific structures in the Arnold web so that by properly tuning the laser frequency we can control the dissociation dynamics. Back