A direct comparison of vibrational deactivation of hexafluorobenzene excited by infrared multiple photon absorption and internal conversion

We report the first direct comparison between energy transfer parameters measured using infrared multiphoton absorption (IRMPA) versus ultraviolet (UV) excitation followed by rapid internal conversion (IC). Highly excited hexafluorobenzene (HFB) molecules in the electronic ground state were prepared by (i) IRMPA by CO2 laser pumping to an average initial energy of 14500-17500cm-1 and (ii) UV excitation to ∼40300cm-1 followed by IC. The vibrational deactivation of the highly excited HFB by the monatomic collider gas argon was monitored by time-resolved infrared fluorescence. The results for the two methods are identical within experimental error, demonstrating the viability of IRMPA as a method of state preparation for vibrational deactivation experiments involving large molecules. © 1998 American Institute of Physics

Diagnostics of Air Purification Plasma Device by Spatially Resolved Emission Spectroscopy

A non-thermal plasma, air purification device (PlasmaShield®, MD250, Keswick, SA, Australia), was investigated using spatially resolved optical emission spectroscopy. The emission spectra were measured with two spatial dimensions to analyze and identify the transition lines of excited NO–γ (A2Σ–X2Π), N2 (C3Π–B3Π), and N2+ (B2Σ–X2Σ) systems. The N2 emission band at 337 and 316 nm were used to determine the spatially resolved vibrational temperature of N2 molecules, TvibN2. It was found that the average N2 vibrational temperatures in the x and y directions are almost the same. Two key operating parameters, supplied power and air flow, influence the N2 vibrational temperature. The results demonstrate that applying higher supplied power increases the vibrational temperature, while changes in air flow velocity do not affect the vibrational temperature values. The phenomenological plasma temperature (PPT) was also estimated from the N2 vibrational temperature. It was observed that PlasmaShield® generates excited N2 and NO only within a narrow region around the discharge electrode tip (with peak intensity below 100 µm from the tip). The study also shows no presence of excited OH*, O*, and other radicals

Isotope Detection in Microwave-Assisted Laser-Induced Plasma

Isotope detection and identification is paramount in many fields of science and industry, such as in the fusion and fission energy sector, in medicine and material science, and in archeology. Isotopic information provides fundamental insight into the research questions related to these fields, as well as insight into product quality and operational safety. However, isotope identification with established mass-spectrometric methods is laborious and requires laboratory conditions. In this work, microwave-assisted laser-induced breakdown spectroscopy (MW-LIBS) is introduced for isotope detection and identification utilizing radical and molecular emission. The approach is demonstrated with stable B and Cl isotopes in solids and H isotopes in liquid using emissions from BO and BO2, CaCl, and OH molecules, respectively. MW-LIBS utilizes the extended emissive plasma lifetime and molecular-emission signal-integration times up to 900 μs to enable the use of low (~4 mJ) ablation energy without compromising signal intensity and, consequently, sensitivity. On the other hand, long plasma lifetime gives time for molecular formation. Increase in signal intensity towards the late microwave-assisted plasma was prominent in BO2 and OH emission intensities. As MW-LIBS is online-capable and requires minimal sample preparation, it is an interesting option for isotope detection in various applications

Exploring Sensitive Label-Free Multiplex Analysis with Raman-Coded Microbeads and SERS-Coded Reporters

Suspension microsphere immunoassays are rapidly gaining attention in multiplex bioassays. Accurate detection of multiple analytes from a single measurement is critical in modern bioanalysis, which always requires complex encoding systems. In this study, a novel bioassay with Raman-coded antibody supports (polymer microbeads with different Raman signatures) and surface-enhanced Raman scattering (SERS)-coded nanotags (organic thiols on a gold nanoparticle surface with different SERS signatures) was developed as a model fluorescent, label-free, bead-based multiplex immunoassay system. The developed homogeneous immunoassays included two surface-functionalized monodisperse Raman-coded microbeads of polystyrene and poly(4-tert-butylstyrene) as the immune solid supports, and two epitope modified nanotags (self-assembled 4-mercaptobenzoic acid or 3-mercaptopropionic acid on gold nanoparticles) as the SERS-coded reporters. Such multiplex Raman/SERS-based microsphere immunoassays could selectively identify specific paratope–epitope interactions from one mixture sample solution under a single laser illumination, and thus hold great promise in future suspension multiplex analysis for diverse biomedical applications

Mid-IR polarization spectroscopy applied for detection of methane at atmospheric pressure

Methane was studied with mid-infrared polarization spectroscopy (PS) in an atmospheric gas jet. Detection limit was investigated and laser induced fluorescence and PS spectra for the P, Q, and R branch are presented

Effect of hydrothermal carbonisation temperature on the ignition properties of grape marc hydrochar fuels

The ignition properties of solid hydrochars and their slurries derived from the hydrothermal carbonisation (HTC) of grape marc were evaluated and compared using radiation heating methods. Solid hydrochar samples produced at 180 ◦C , 220 ◦C and 260 ◦C with median particle sizes of 10 – 14 μm were mixed with water to prepare the hydrochar slurries for ignition experiments. The 260 ◦C solid hydrochar exhibited the shortest ignition delay time (0.2 s) and the lowest ignition temperature (179 ◦C). It might be due to the presence of secondary char, which was evident by a unique peak appearing in both thermogravimetric and radiation heating profiles of the 260 ◦C solid hydrochar. This property also demonstrated a significant impact on the combustion characteristics of its slurry. The 220 ◦C solid hydrochar was ignited after the 260 ◦C solid hydrochar (0.28 s) while its slurry experienced the longest ignition delay time among the rest (2.38 s). These observations could be related to the hydrophilic content on the outer layer of 220 ◦C solid hydrochar. This hydrochar and its slurry, however, ignited at the similar temperature with the 180 ◦C solid hydrochar and its slurry respectively, indicating that the volatile matter content had a more significant effect on the ignition temperature of the 220 ◦C solid hydrochar than its hydrophilic components. Results from this study further demonstrated that the hydrochar slurry derived from grape marc is highly ignitable which might provide an alternative pathway to recycle grape marc into a sustainable liquid fuel.Duong Nguyen, Wanxia Zhao, Mikko Makel, Zeyad T. Alwahabi, Chi Wai Kwon

Real-time release of Na, K and Ca during thermal conversion of biomass using quantitative microwave-assisted laser-induced breakdown spectroscopy

Power production with thermal conversion has met new challenges due the global pressure to use CO2 neutral and renewable fuels, e.g. recycled fuel and biomass. Many of these fuels contain high concentrations of elements, such as alkali metals and chlorine, that together are harmful for boiler structures and may cause operational problems. Therefore, detailed quantitative information on release behaviour of the problematic elements, potassium and sodium, is required. For this, a new burner, which allows linear calibration of laser induced breakdown spectroscopy (LIBS) measurement towards higher concentrations relevant for the release studies during thermal conversion of biomass, was designed. The analytical performance of conventional LIBS measurement is significantly improved by introducing microwave radiation to the laser-induced plasma. An enhancement of linearity and up to 60-fold improvement of limit of detection (LOD) was observed with microwave-assisted LIBS (MW-LIBS) in comparison to conventional LIBS. The LOD of Na, K and Ca were 10 ppb, 19 ppb and 16 ppb, respectively. In-flame MW-LIBS measurement was applied to record time-traces of K, Na and Ca during thermal conversion of a poplar pellet. This is the first demonstration of Microwave near-field applicator injected MW-LIBS for gas phase measurement. With broad dynamic measurement range, the proposed method can be applied to extensive research of elemental release behaviour of different fuels. In addition to combustion studies, the MW-LIBS method can be extended to study trace-elements in gas phase in different fields of industry and science.acceptedVersionPeer reviewe