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Microwave spectroscopy is a technique in which the absorption of radiation in rotational transitions of small molecular species is detected and the resonant frequencies are measured to great accuracy (8 to 9 significant digits). Using quantum mechanics the frequency data can be fit to a model Hamiltonian, and the molecular structure and other molecular properties can be determined with great precision. Intensities and widths of microwave lines provide concentrations and dynamical information. We have applied this technique in laboratory discharge plasmas to transient species like the CN radical the HNC unstable molecule, the a3P metastable electronic state of CO, and especially to molecular ions like CO+, HCO+, HOC+, HNN+, HCS+, KrD+, XeH+, SO+, H2D+, SiF+, or PO+. Many of these species are of great importance in the chemistry of the interstellar medium and have been detected by radioastronomy (actually microwave astronomy), in some cases with our active participation. A great deal of information on the chemistry and dynamics of the interstellar medium has been obtained by radioastronomical study of species like these. The chemistry and dynamics of the laboratory discharges themselves is also of great interest and only partially understood. We are trying to improve this understanding using microwave spectroscopy and other techniques at our disposal. The latter include a quadrupole mass spectrometry, a high resolution ultraviolet-visible emission spectroscopy, and computer controlled Langmuir probes. We are also carrying out large scale quantum chemical calculations of the structures and other properties of small ions and molecules. Many species have been treated with large basis sets (80"100 contracted orbitals) and correlated ab initio methods like CI-SD, MP4-SDQ, CEPA"1, and CASSCF. Results are used to facilitate spectroscopic searches for new ions and also to compare against our experimentally determined spectroscopic constants. Another part of our research involves active participation in the Engineering Research Center for Plasma Aided Manufacturing. Plasma etching and deposition are crucial steps in the manufacture of almost all semiconductor devices, and we are working to understand the details of the chemistry and physics of the plasmas used. Diagnostics like ultra-high resolution infrared diode laser spectroscopy and laster induced fluorescence spectroscopy, laser induced fluorescence spectroscopy, and microwave spectroscopy are being used to probe plasmas in RF (13 MHz) discharge and microwave (2450 MHz) electron cyclotron resonance (ECR) plasma reactors.