TRANSIENT SPECTROSCOPY AND DYNAMICS OF OPTICALLY CENTRIFUGED MOLECULES

Abstract

This dissertation investigates the behavior of molecules with extreme amounts of rotational energy and oriented angular momentum. The molecules studied in this thesis are prepared in an optical centrifuge and are studied using high-resolution transient IR absorption spectroscopy. The optical centrifuge uses intense, shaped laser pulses to accelerate molecules angularly into extreme rotational states. Through the interaction with the field, anisotropic molecules are trapped and follow the field through its angular acceleration. The final angular frequency of the molecules depends on the spectral profile of the centrifuge. The result is an ensemble of molecules with highly oriented angular momentum and rotational energies far from that of equilibrium. High-resolution transient IR absorption spectroscopy is used to measure nascent distributions of optically centrifuged molecules, as well as the collisional dynamics of the centrifuged molecules as they relax toward equilibrium by means of a collisional cascade.

These studies show that an optical centrifuge can launch N2O molecules into rotational states with J≥195, and that the mechanism for collisional energy transfer depends on the rotational energy and angular momentum of the molecules. We show that our optical centrifuge is capable of driving CO2 into rotational states up to J= 280, and we measure spectral perturbations that have not been observed previously. We measure the full rotational distribution of centrifuged CO and show that states up to J= 80 are populated using the full centrifuge bandwidth. This study of CO provides a lower limit to the final angular frequencies of N2O and CO2 prepared in our optical centrifuge. We have developed a tunable optical centrifuge to measure directly the nascent population distributions of centrifuged molecules, from which the capture and acceleration efficiencies for CO and CO2 are compared. Lastly, the effect of reactant rotational energy on bimolecular reactions is investigated. We control the rotational energy in CO reactants and measure the yield of C2 products. We find that CO rotational energy inhibits bimolecular reactions that form C2. This work provides new information about the properties and behavior of molecules in a previously inaccessible energy regime and lays the groundwork for future investigations.