Chiral Molecular Beams, Quantum Tunneling and Improved Microwave Spectroscopy

Harvard University, Cambridge MA

Investigators

Abstract

With this award, the Chemical Measurement and Imaging Program of the Division of Chemistry is supporting Professor John Doyle of Harvard University to study molecular chirality through advances in molecular beam techniques and interrogation with microwave spectroscopy. Atoms and molecules are the basic building blocks of all substances. Understanding their essential behavior is necessary for a full understanding of chemical processes, including those underlying living systems. In living cells, many molecules have a fundamental 'twist', very similar to the direction of spiral ridges on a screw. Just like a screw, the direction of the molecular spiral, known as 'chirality', determines function. For normal screws ('right handed' ones), if you turn them clockwise they tighten; a 'left handed' screw would loosen. This is a very pronounced effect in molecules also. For example, many new drugs have a single handedness (i.e. chirality). In order to understand the basic behavior of molecules, their chirality must be detectable. In this project researchers will use their newly discovered tool for measuring chirality to study fundamental quantum behavior of chirality in molecules. In particular, they will look for the slow transformation of a molecule with a spiral in one direction to a molecule with a spiral in the opposite direction. This effect can only be described by the fundamental theory of the microscopic realm, quantum mechanics. Researchers in the Doyle group will test these predictions and in carrying out these studies gain valuable experience in modern physical and analytical chemistry research. In order to study chirality of molecules, the Doyle group will use molecular beams and interrogate these with microwave radiation. The molecular seams will be generated by injecting them through a small hole into a nearly perfect vacuum. This will form a stream of molecules that have no interactions 'a nearly pristine physical setup' except with the applied electromagnetic radiation. The molecules that will be studied have electric dipoles (similar to a bar magnet, except with electric charge on the North and South poles). These dipoles will absorb and emit radiation in the microwave regime. By creating a screw-type pattern of microwave radiation, the molecule can be caused to emit radiation that depends on the direction of the spiral (chirality) of the molecules. This is similar to testing if a screw is left or right handed by trying to insert it in a right-handed screw hole. The researchers will initially prepare molecules of one chirality (e.g. right handed) and then use microwaves to see if they transform into the other chirality (left-handed). Comparison with theory will be done to test our understanding of this fundamental phenomenon.