William A. Burns

Infrared laser spectroscopy of jet cooled cobalt tricarbonyl nitrosyl.

Rotationally resolved infrared absorption spectra for the 1(0)(1) band of jet cooled cobalt tricarbonyl nitrosyl have been observed and analyzed. Several longitudinal modes of a Pb-salt diode laser were utilized to measure 105 rovibrational transitions for this particular vibrational band centered near 2112 cm(-1). Spectra were optimized using both argon and helium carrier gases and these experiments eventually led to rovibrational transitions being assigned to four different K subbands, specifically the K = 0, 3, 6, and 9 subbands. An iterative least-squares analysis of the spectroscopic data yielded the following molecular parameters nu0 = 2111.7457(9) cm(-1), B0 = 0.034747(12) cm(-1), B1 = 0.034695(15) cm(-1), C1 = 0.03380(9) cm(-1), and D1K = 6.3(9) x 10(-6) cm(-1) (where 3sigma uncertainties are listed in parenthesis).

Spectral signatures for volatile impurities in TNT and RDX based explosives

Vapor phase sensing and detection of TNT-based explosives is extremely challenging due in part to the low vapor pressure of TNT. We believe one effective strategy for optically based sensing of TNT-based explosives involves focusing not on the spectral signature for pure TNT, but rather on a more volatile series of compounds that are present in TNT as impurities. To date we have catalogued and reported a number of rotationally resolved infrared transition frequencies for nitrobenzene, toluene, o-nitrotoluene, and m-nitrotoluene in the 14 micron region. Here we describe the use of an in-house spectral calibration program that while designed for calibration of Pb-salt diode laser spectra, is quite general and could be utilized for many spectroscopic detection and/or analysis applications. Finally, a sensing measurement for a volatile organic impurity related to RDX-based explosives such as C4 is presented and discussed.

Optical detection of explosives: spectral signatures for the explosive bouquet

Research with canines suggests that sniffer dogs alert not on the odor from a pure explosive, but rather on a set of far more volatile species present in an explosive as impurities. Following the explosive trained canine example, we have begun examining the vapor signatures for many of these volatile impurities utilizing high resolution spectroscopic techniques in several molecular fingerprint regions. Here we will describe some of these high resolution measurements and discuss strategies for selecting useful spectral signature regions for individual molecular markers of interest.

Measurement of ammonia skin gas using a mid-infrared Pb-salt tunable diode laser

The concentration of Ammonia excreted through human skin has recently been measured using a gas chromatograph equipped with a flame ionization detector (GC-FID) by a group from Nagoya, Japan. These emissions, referred to as ammonia skin gas, were determined to be 1.7±.4 ng/cm3 for healthy subjects in the study. To achieve greater molecule specificity, sensitivity, as well as add a real time capability, we are investigating the potential of a mid IR laser spectrometer, consisting of a Pb-salt diode laser coupled with a low volume 75 meter Herriott gas sample cell, to perform real time ammonia diagnostic measurements. Here we will present a series of preliminary ammonia skin gas measurements obtained with this mid IR laser system.

Spectral signatures for RDX based explosives in the 3 micron region

Explosive compounds such as RDX, and HMX present significant challenges to optically based sensors. This difficulty is due in part to the low vapor pressures these compounds possess. One approach for sensing explosives that circumvents the low explosive vapor pressure problem, involves focusing on the trace amounts of relatively high vapor pressure impurities that will be present in the vapor signature. In order to effectively detect these volatile impurities, the spectral signature databases must be readily available. One of our goals therefore, is the generation of a database of high resolution spectral signatures for these volatile organic impurities. Some rather formidable spectroscopic measurement challenges have been encountered while working to extend the spectral signature effort to the 3 micron region. Here we will outline progress to date, with a focus on the volatile organic compounds formaldehyde, acetaldehyde, nitromethane, acetone, isobutene, and cyclohexanone.