טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAkiva Amit
SubjectTransfer of Vibrational Excitation through Hydrogen
bonds
DepartmentDepartment of Chemistry
Supervisor Dr. Lev Chuntonov
Full Thesis textFull thesis text - English Version


Abstract

Spectroscopic studies of molecular systems involving hydrogen bonding has been at the forefront of fundamental chemical and physical research for many decades. Linear infrared spectroscopy provides information on the molecular vibrational transition frequencies and their bandwidth, which in turn reflect molecular structure and its environment. Nonlinear infrared spectroscopy, provides further details including the time scales of ultrafast molecular dynamics, which are highly important for understanding molecular interactions. We conducted third-order nonlinear ultrafast vibrational spectroscopy study of a homologue series of phenol molecules with chlorine substituents in nonpolar solvents. Substituted phenols are known to serve as a convenient benchmark system in chemistry. Here, we explored the ground state molecular dynamics of phenols using infrared spectroscopy of the hydroxyl stretching vibrational mode (OH). In our experiments, we characterized various aspects of ultrafast vibrational dynamics of the OH modes, including their vibrational relaxation, rotational diffusion, and pure dephasing. We identified possible excitation relaxation pathways and dephasing mechanisms. Using predictions of the Kubo-Oxtoby theory for pure dephasing, we identified a mechanism of protection of the excited OH oscillator from fluctuating forces exerted by the solvent through intra-molecular hydrogen bonding. Such an effect can be relevant for ultrafast dynamics in biomolecules, where H-bonding plays a central role.