Fundamentally not requiring a vacuum chamber, atmospheric pressure glow discharges (APGDs) offer an exciting prospect for a wide range of material processing applications. To characterize their operation and establish their operation range, a radio frequency (rf) APGD is studied experimentally with measurement of discharge voltage, current, dissipated plasma power and plasma impedance. Different from the current understanding that rf APGD are operative only in the abnormal glow mode, we show the presence of two additional modes namely the normal glow mode and the recovery mode. It is shown that all three modes are spatially uniform and possess key characteristics of a glow discharge. So rf APGD have a much wider operation range than previously believed. To provide further insights, we investigate the transition from the abnormal glow mode to the recovery mode. It is established that the cause responsible for the mode transition is sheath breakdown, a phenomenon that is known in low- and moderate-pressure glow discharges but has not been reported before for atmospheric-pressure glow discharges. Finally we demonstrate that plasma dynamics, hence plasma stability, in these three modes are influenced crucially by the impedance matching between the plasma rig and the power source.

In this paper, the UV Raman spectra of a large number of saturated and alkyl-substituted monocyclic, bicyclic and polycyclic aromatic hydrocarbons are obtained at 220 and 233 nm excitation wavelengths. Also included are nitrogen- and sulphur-containing hydrocarbons. The spectra obtained are fluorescence free, even for such highly fluorescent compounds as perylene, consistent with earlier reports of UV Raman spectra of hydrocarbons. The hydrocarbon UV Raman spectra exhibit greatly improved signal-to-noise ratio when in the neat liquid or solution state compared with the neat solid state, suggesting that some surface degradation occurs under the conditions used here. Assignments are given for most of the bands and clear marker bands for the different classes of hydrocarbons are readily observable, although their relative intensities vary greatly. These results are discussed in the context of structure and symmetry to develop a consistent, molecular-based model of vibrational group frequencies.

Raman and resonance Raman spectroscopy with ultraviolet excitation were performed on several sample types of oilsands-derived bitumen, highly heterogeneous mixtures of hydrocarbons, and commercial gasoline samples. Only excitation wavelengths below ∼240 nm successfully yielded fluorescence-free Raman spectra on all of the samples tested. The spectra were surprisingly simple in the 800–1800 cm−1 region, with most of the samples yielding spectra containing only 2 bands. The results presented here tentatively suggest that ultraviolet (UV) Raman spectroscopy in the “fingerprint” spectral regions will be useful for the qualitative identification of saturate, mono-, bi-, tri-, and polycyclic aromatic hydrocarbons. Tentative marker bands for total aromatic, saturate, mono-, and bicyclic (or higher) aromatic hydrocarbons are clearly observed at ∼1600, <900, 1036, and ∼1380 cm−1, respectively. Observed relative intensities vary with the excitation wavelength from 220 to 234 nm, suggesting that some selectivity is achievable by wavelength tuning. Preliminary investigations of commercial gasoline samples indicate that UV Raman spectroscopy can be used for refinery/vendor identification of unknown gasoline samples.

UCIO4, ksait-% = 1.2), small substituent effects (kcgH5C(Me)OHCo2H: kceH5cHOHco2H:kpx:H3CeH4CHOHCo2H = 0.91:1.0:1.2), and relative insensitivity to solvent polarity (small and parallel rate changes with cosolvents, acetic anhydride, acetonitrile, and benzene) argue against pathways involving rate-determining ionization.3 Furthermore, none of the observations indicating a free-radical pathway for the decarboxylation of monofunctional carboxylic acids, (1) induction times and sigmoidal rate profile with time, (2) very strong inhibition by oxygen in every case, (3) increased rates with uv illumination, and (4) radical trapping, were observed during mandelic acid cleavage by Pb(OAc)4 in acetic acid solvent. Parallel runs using degassed samples in an oxygen-free atmosphere had virtually identical rates with those exposed to the atmosphere; also, bubbling air through a degassed sample did not change the rate of oxidative cleavage. Decarboxylations of pivalic, phenylacetic, and acetic acids all yielded free radicals which were trapped by acrylonitrile. In contrast, no radicals could be detected during the cleavage of mandelic acid under identical conditions. Similarly, Trahanovsky5 differentiated between free-radical and non-free-radical mechanisms for glycol cleavage by Celv and Pb(OAc)4, respectively, by trapping radicals with acrylamide during the cerium(IV) oxidation. None could be detected during the lead tetraacetate cleavage.(5) W.