Lecture, four hours; outside study, eight hours. Introduction to science that governs interaction of light and matter (in gas phase). Review of key concepts of physical gas dynamics to establish microscopic or molecular perspective (non-continuum perspective) on gas properties and physical behavior. Material is structured within three subtopics of gas-phase spectroscopy: spectral line positions, spectral line intensities, and spectral line shapes. These capture spectroscopic interactions of atoms, diatomic molecules, and polyatomic molecules, and their respective rotational (THz), vibrational (IR), and electronic (UV/Vis) spectra. Presentation of absorption, emission, and scattering processes, associated optical measurement techniques. Integration of subject matter from physical sciences (quantum mechanics, statistical thermodynamics, and physical chemistry), covered at level appropriate for engineer. Letter grading.