Low-Cost, Balle-Flygare-Type Cavity Fourier Transform Microwave Spectrometer and Pure Rotational Spectroscopy Laboratory for Teaching Physical Chemistry and Astronomy

Few laboratory exercises exist that introduce undergraduate students to both the concepts and instrumentation used in rotational spectroscopy. Because of this gap in undergraduate laboratory training, a teaching laboratory for the pure rotational spectroscopy of benzonitrile has been developed and reported. Owing to benzonitrile's recent discovery in space, the molecular spectroscopic technique and target are applicable to both the physical chemistry and astronomy disciplines. Because of the size of the dipole moment and relative safety of the molecule chosen, the laboratory approach allows undergraduates to directly load, tune, measure, and assign spectra using the same quantum chemical approaches and spectroscopic assigning tools available to a researcher in the field. Concepts taught in this laboratory include the rigid and semirigid rotor, as well as low-level nuclear electric quadrupole coupling Hamiltonians. To minimize the budget and allow the students to get hands-on training with the rotational spectroscopy instrumentation, an interactive, low-cost, Balle-Flygare-type, cavity Fourier transform microwave (FTMW) spectrometer of research-grade quality was developed and is reported. Implementation of the laboratory exercise, time of exercise, and student response to the exercise is also reported.