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Molecular Dynamics Study in the Interaction of Intense Femtosecond Laser Pulse with Methane Molecule

Irani, Elnaz | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 46019 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Sadighi-Bonabi, Rasul; Anvari, Abbas; Asgari, Reza
  7. Abstract:
  8. In this project, the ionization and dissociation of methane molecule by intense femto-second lasers has been studied. Dissociation probability is calculated for interacting CH4 molecule under Ti: Sapphire laser pulse with pulse durations of 10- 40fs in intensities at the range of 1014-1016 Wcm-2. Calculations are carried out with time-dependent density functional theory using Gaussian03 and Octopus packages as powerful computational chemical physics programs. Due to importance of the dependence of interaction dynamics to laser parameters, the effect of these parameters including different intensities, polarization, various pulse durations and pulse envelopes are investigated. The optimal effective parameters are evaluated to achieve the maximum dissociation probability. The optimum field is found and it is giving 71% dissociation probability for Gaussian envelope and 40fs (FWHM) at 1016 Wcm-2. The dissociation probability is also calculated by optimum convolution of dual short pulses. These results are compared with the available experimental measurements. Furthermore, the time dependent electron localization function, the time evolution of dipole moment and the electron density are presented to analyze the time evolution of molecular dynamics. By simple semi-classical Ehrenfest molecular dynamics, time variation of bond length, velocity and Orientation effect are presented. Advances in recent laser technologies have promoted the possibility of the generation of arbitrary laser pulses with manipulation of amplitude, phase and spectrum elements. Quantum optimal control theory provides the useful tool to optimum design of the laser pulses capable of controlling a quantum system towards prescribed products of 2CH2+, 1CH+, 2C+ and 1C++ with conversion yields of up to 75%. The dissociation pathways for selective ionic fragmentations are implemented and an exact energy diagram is presented.
  9. Keywords:
  10. Femtosecond Laser ; Methane Dissociation ; Time Dependent Density Functional Theory ; Quantum Optimal Control ; Methane Molecule Ionization

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