Jim O’Brien is an experimental physical chemist who specializes in fundamental and applied high-resolution laser spectroscopy and in gas phase analytical chemistry. The primary tool employed is Intracavity Laser Spectroscopy. ILS techniques provide tremendously enhanced sensitivity for obtaining quantitative absorption spectra. Research areas include the acquisition of quantitative absorption spectroscopy parameters (e.g., absorption coefficients for methane in the visible to near-IR spectral region to assist in interpreting spectra of the outer planets such as Neptune and line positions for the high-resolution spectrum of molecular O2 for visible and near-IR bands;  high-resolution electronic spectroscopy of small molecules (e.g., CuCl, NiCl, NiH) with a view to locating excited electronic states in these species; the gas phase chemistries and species involved in a variety of chemical vapor deposition (CVD) processes (e.g., the plasma deposition of films of diamond-like carbon (DLC), diamond-like nanocomposites (DLN), and silicon oxide); and  the further development of the intracavity laser spectroscopy (ILS) technique for analytical purposes (e.g., in acquiring spectra at ultra-high spectral resolution) and its range of applications (e.g., extension of ILS into the IR region by use of fiber lasers).