Far Infrared Fourier Transform Spectrometer for Undergraduate Physics Experiments

Colby College, Waterville ME

Investigators

Abstract

Physics (13) The motions of atoms within a molecule or a crystal lattice constitute one of the most fundamental physical phenomena of multi-atom systems, yet few undergraduate physics curricula include experimental studies of vibrational properties. Modern spectrometers can measure frequencies into the far infrared using the Fourier Transform method and are well suited to operation by trained undergraduates. In this project, students are using a far infrared (FIR) Fourier Transform (FT) spectrometer in undergraduate physics experiments, so that they will become familiar with this important technique and see basic physics concepts brought to life. The spectrometer is being used to enhance the laboratory component of the Modern Physics course, to overhaul the Experimental Condensed Matter Physics course, to expand the number of student-faculty research projects, and to engage in collaborations with the Chemistry Department. Students are progressing from studying vibrations of diatomic molecules in the gas phase, to vibrations of large fullerene cages imbedded in a molecular solid, to phonons in simple ionic crystalline lattices. The second year Modern Physics laboratory is incorporating an expanded version of a classic experiment in rotations and vibrations of gas phase HCl. The dual far and middle infrared capability of the instrument allows students to observe excitations of pure molecular rotations at low frequency, and recognize them again as fine structure on top of vibrations in the middle infrared region. Two experiments in FIR vibrational spectroscopy are effecting a major revamping of the advanced Experimental Condensed Matter Physics course. The first, adapted from the research literature and the undergraduate work of students at the L. Eotvos University and the Technical University of Budapest, demonstrates the central role of symmetry in determining vibrational properties of pristine and photo-polymerized c60. The second, based on an experiment that was recently implemented at Reed College, connects a simple 1D lattice dynamics calculation to the observation of optical phonon modes in a real physical system. Another goal of this project to take advantage of an opportunity to reach an unprecedented number of women physics majors at Colby, as indicated by pre-registration numbers for the fall 2000 Modern Physics course. By providing an exceptional undergraduate program of experimental physics, we hope to further the careers of these young women, inspire them to become role models for others, and maintain a critical mass of women in the program. Evaluations of the project will consider specifically their impact on female students as well as on student learning in general. Students will disseminate the results at conferences for undergraduates, and in education or research journals, as appropriate for the work.