Chemistry Department Seminar

In our lab at UNCG we have implemented a molecular beam experiment that takes advantage of new millimeter / sub-millimeter wavelength technology in order to probe the products of photodissociation with ultrahigh energy resolution.1 The comparatively simple and inexpensive setup demonstrates the utility of combining commercial solid-state millimeter / sub-millimeter wavelength sources with hot-electron bolometer detectors to directly probe parent and product hyperfine rovibronic levels and their Doppler-resolved velocity distributions in a molecular beam. For example, in open-shell products with nuclear spin, the ultrahigh energy resolution of the rotational spectroscopy easily resolves nuclear quadrupole hyperfine structure and lambda doublets in both ground and excited spin-orbit states as well as in ground and excited vibrational levels. In this talk the technique is applied to the mode-specific photodissociation of OClO which has been the subject of many experimental and theoretical studies, driven in large part by the role it plays as a reservoir of free chlorine atoms in the stratosphere. The UV absorption spectrum of OClO from 270 to 470 nm displays a well-defined progression of predissociative vibrational levels in the excited A 2A2 electronic state. In the gas phase, it had been found that >96% of the parent molecules dissociate by the ClO (X 23/2,1/2) + O (3PJ) product channel and that the internal vibrational energy of the ClO product increases nearly linearly with increasing parent excitation.2,3 The photodissociation of OClO not only offers an opportunity test the experiment on a well-characterized molecular system, it is also particularly useful for demonstrating the type of dynamical information that may be extracted from the experiment and the extremely fine detail that may be achieved. Preliminary spectra from the experiment probe the product molecule’s electronic, vibrational, rotational, lambda doublet, and hyperfine state distributio