The internal energy distributions, P(epsilon), of a millisecond pulsed radio frequency glow discharge plasma were investigated using tungsten hexcarbonyl W(CO)(6) as a "thermometer molecule". Vapor of the probe molecule, W(CO)(6), was introduced into the plasma and subjected to various ionization and excitation processes therein. The resultant molecular and fragment ions were monitored using a Time-of-Flight mass spectrometer. Ion abundance data were utilized in combination with the known energetics of W(CO)(6) to construct the P(epsilon) plots. The P(epsilon) of W(CO)(6) exhibited strong temporal dependence over the pulse cycle: Distinct internal energy distributions were found at the discharge breakdown period (prepeak), the steady state period (plateau), and the post-pulse period (afterpeak). Spatial variation in P(epsilon) was also observed, especially during the plateau regime. The observations suggest that this pulsed glow discharge affords excellent energy tunability that can be used to perform selective ionization and fragmentation for molecular, structural, and elemental information. Parametric studies were performed to evaluate the effects of discharge pressure and operating power on P(epsilon). These studies also provided insight into the correlation of the observed P(epsilon)s with the fundamental ionization and excitation mechanisms in the plasma. The temporal and spatial variations in P(epsilon) were hence attributed to changes in the dominant energy transfer processes at specific times in specific regions of the plasma. These data will be useful in future efforts to optimize the analytical performance of this source for chemical speciation.

A series of bromine-containing flame-retardant plastics was used to demonstrate the applicability of pulsed radio frequency glow discharge mass spectrometry to the determination of elements in commercial polymers. The direct analysis of bulk samples produced both atomic and molecular species, allowing elemental identification and molecular characterization. However, the low ion signal intensities hindered quantification. Atomization mechanisms for the plastic samples were studied in detail using scanning electron microscopy and mass spectrometry. Although some thermal desorption was observed, sputter atomization dominated when samples were not subjected to excessive discharge power. The sputter rates of various polymers, as evidenced by sputter weight loss measurements, showed a strong correlation with their ion production capabilities. Sputtering rates were related to the physical and chemical properties inherent to a polymer's composition. Analysis of samples compacted with a silver binder provided intense analyte signals allowing quantitative analysis. Signal stability, measurement accuracy, measurement precision, and detection limits were all assessed.

Interpretation of optical emission spectra reveals the primary excitation mechanisms for discharge gas, argon and sputtered analyte, copper, species in glow discharge plasmas operated with millisecond pulses of radiofrequency or direct current power. There is negligible difference between the two power sources. During the applied power pulse, plasma processes include ion and atom excitation through electron excitation, asymmetric charge exchange and Penning ionization. Fast ion and atom excitation processes, characterized by monitoring argon emission at 811.5 nm, occur within 2 mm of the cathode surface. Electron excitation, for both discharge gas and sputtered species, maximizes 3 mm from the cathode surface. Asymmetric charge exchange between ground state sputtered atoms and discharge gas ions, characterized by Cu II emission at 224.7 nm, occurs at 5 mm from the cathode surface. Upon power termination, the recombination of ions with thermal electrons yields excited atoms and argon metastable species. At this time, emission monitored at 811.5 nm maximizes 6-7 mm from the cathode surface, corresponding to an increase in the metastable population and, hence, Penning ionization.