Time-resolved number densities of excited electronic state of nitrogen, N₂(A³Σ_u⁺,v=0,1,2), have been measured in a nanosecond pulse discharge using Cavity Ring-Down Spectroscopy (CRDS). The CRDS spectrometer is operated using a 10 Hz Nd:YAG laser which pumps a narrowband tunable dye laser using a LDS765 dye, to produce output between 745 to 770 nm with a linewidth of 0.12 cm⁻¹. The ring-down cavity is a 10 mm x 22 mm rectangular cross section quartz channel 55 cm long, fused to two 1.5 inch diameter quartz tubes at both ends, with the total cavity length of 90 cm. The mirrors (reflectivity of 0.99995) are attached to the ends of the ring-down cavity using stainless steel adjustable mounts, for precision alignment. Two rectangular plate copper electrodes, 12 mm x 60 mm, are attached to the top and bottom walls of the quartz channel in the middle of the cavity, using silicone rubber adhesive. The electrodes are powered by a custom-built high-voltage pulse generator producing alternating polarity pulses with peak voltage up to 15 kV and pulse duration of approximately 100 ns FWHM. The pulser is operated in burst mode, with burst repetition rate of 10 Hz, pulse repetition rate of 10 kHz, and 10 pulses per burst, with coupled discharge energy of approximately 0.3 mJ/pulse. Spectra of N₂(B³Π_g←A³Σ_u⁺,v) absorption bands are taken 25 μs after the last discharge pulse in the burst, with all absorption transitions identified. Time resolved CRDS data are taken from isolated rotational lines for each vibrational state to infer temporal evolution of absolute populations of vibrational levels of N₂(A³Σ_u⁺) at t=25-1500 μs after the last discharge pulse. This diagnostics is being developed for measurements of excited metastable state populations of N₂ and O₂ in nonequilibrium plasmas and nonequilibrium high-speed flows.

A recently implemented cavity ring-down spectrometer has been used to perform absolute number density measurements of hydroperoxyl radical (HO₂) generated in a repetitive nanosecond-duration, pulse discharge sustained in a mixture of H₂/O₂/Ar. The probe source for the spectrometer is a custom-built, injection-seeded, optical parametric oscillator emitting an idler beam in the 1500 nm region accessing the first overtone (2ν₁) of the O-H stretch. Water vapor was used as a standard species to characterize the spectrometer and provide estimates of the spectral linewidth, sensitivity, and noise level. A specially constructed ring-down cell, with the central portion consisting of rectangular quartz channel tubing and a pair of copper plate electrodes, was used to produce a repetitively pulsed discharge in a H₂/O₂/Ar mixture. Narrow bandwidth cavity ring down spectra are acquired of a hydroperoxyl absorption feature composed of numerous closely spaced ro-vibrational lines centered at 6638.20 cm⁻¹and number density is determined from the resulting spectral line. This is believed to be the first detection and quantitative measurement of hydroperoxyl radical produced in a nanosecond pulse discharge. The measured number density is compared to the value predicted by the kinetic model of a nanosecond pulse discharge in a reacting H₂/O₂/Ar mixture.

A high sensitivity sensor, combining a multipass cell and wavelength modulation spectroscopy in the near-IR spectral region ( 1.651μm) was designed and implemented for trace gas detection. The sensor uses a DFB laser and software lock-in detection, realized with a LabVIEW code. The high sensitivity was achieved by combining the multipass cell having a long effective absorption length of 290 meters, the wavelength modulation spectroscopy, and noise suppression by using a dual beam scheme. The developed spectroscopic technique demonstrates an improved sensitivity for methane in ambient air and a relatively short detection time compared to previously reported sensors. The average methane concentration measured in ambient air was 2.01ppm with a relative error of ±2.5%. With Allan deviation analysis, it was found that the methane detection limit of 1.2ppb was achieved in 650s. A modification of this scheme for acetone detection with a mid-IR distributed feedback interband cascade laser with the center wavelength around 3.367μm was also developed, achieving the detection limit was 0.58 ppm with 1s and down to 0.12 ppm with 60s signal averaging. This work was supported by Robert A. Welch Foundation, grant No. A1546, the Qatar Foundation, grant NPRP 8-735-1-154.

Small polar compounds in gasoline have been identified using a BrightSpec Fourier Transform Microwave Rotational Resonance (FT-MRR) spectrometer in the 260-290 GHz band with Headspace Sampling Module. The design of this spectrometer is based on segmented Chirped Pulse Fourier Transform millimeter wave (CP-FTmmW) spectroscopy, which exploits recent advances in digital electronics to allow the measurement of broadband rotational spectra in a few minutes. As part of efforts to determine applications for rotational spectroscopy to petrochemical problems, FT-MRR has been employed to record rotationally resolved spectra of small polar compounds in gasoline. Preliminary analysis of the observed features using the BrightSpec spectral database reveals a rich, but interpretable, pattern, due to the sensitivity of FT-MRR to only polar compounds. The complex hydrocarbon matrix, which in many analytical instruments obscures the signals from low concentration impurities, is nearly invisible in FT-MRR. Spectroscopic and quantitative analyses of detected polar compounds are underway and will be given in this talk.

Over the last few years, confined nanometric systems such as quantum wells, quantum wires and quantum dots (QDs) etc. have become most fascinating and promising research fields in view of their tremendous applications environmental safety [1]. When organic/inorganic material reduces to nano size, their electronic and optical properties drastically change from their bulk form. QDs are such nanocrystals. There are two main categories of QD: core type QDs and core-shell type QDs. Core-shell type QDs show less surface defects, enhanced luminescence efficiencies, photo stability and less toxicity compared to that of core type QDs. CdSeS/ZnS is one of such Core/shell type QD which shows all of the above mentioned advantages over its core structure CdSeS. Optical properties mainly high fluorescence with large quantum yield (QY) (up to 85Development of industries generates numerous heavy metal wastes that can cause direct or indirect harm to the environment and humans. Many hazardous heavy metals, such as copper (Cu), chromium (Cr), lead (Pb), zinc (Zn), nickel (Ni), iron (Fe), cadmium (Cd), mercury (Hg), tungsten (W) and silver (Ag) are toxic to living organism [2]. High percentage of Cr and Pb ions within a living organism may lead to various diseases, such as hypersensitivity, lung cancer, nasal cancer, and many other types of cancer. Therefore, the detections of hazardous metal ions like Cr, Zn and Pb are our prime focus. In the present work, we have synthesized functionalized CdSeS/ZnS core shell QDs using L-glutathione (L-GSH) in view of their application to detect hazardous metal ions and some cancer affected diseased cells. The surface modification of QDs with L-GSH make them available for interaction with the targeted materials, which can be used for the detection of hazardous ions and diseased cells present in water. Prepared functionalized CdSeS/ZnS QDs were characterized and tested with the help of several molecular spectroscopic techniques (UV-Vis spectroscopy and fluorescence spectroscopy) by their fluorescence signals. The present work opens a door to the study of new water soluble and biocompatible QDs by the use of their fluorescence sensing for the detection of hazardous metal ions and living cancer cells. References: [1]M. Ishikawa, V. Biju, Prog. Mol. Transl. Sci., 104 (2011) 53. [2] N. Singla, A. Tripathi, M. Rana, S. K Goswami, A. Pathak, P. Chowdhury, J of Luminescence, 165 (2015) 46-55.

Pear ester (ethyl decadienoate, C₁₂H₂₀O₂) is a molecule used in perfumes and as a food flavoring. It can be obtained from both natural and synthetic sources. The motivation for this study was the interest of a local distillery (Vitae Spirits) in understanding differences in the composition of pear ester samples that might cause off flavors in their spirits. Different samples were analyzed by broadband rotational spectroscopy in the attempt to identify possible impurities. The measurement uses a head space sampling approach where the liquid sample is held in a reservoir and heated. The vapor pressure above the sample is entrained in inert neon gas, and this gas mixture is injected into the spectrometer using a pulsed valve. One challenge in the analysis of chemical mixtures using broadband rotational spectroscopy is that the measured spectrum contains overlapping rotational spectra of each mixture component, making it difficult to isolate the spectral pattern of a single chemical species. To aid the analysis, a version of temperature programmed spectroscopy was performed, where the head space spectrum was acquired for a series of sample reservoir temperatures. This measurement method produces characteristic intensity vs. temperature profiles for transitions from a single species. This makes it possible to separate the overall measurement into spectra arising from different species and is an analysis process that can be fully automated. The analysis of different pear ester samples will be summarized including the ability to identify impurity species, like n-hexanal. The identification of pear ester posed challenges in its own right due to the conformational flexibility of the molecule. The approach to obtaining accurate quantum chemistry estimates of the rotational spectrum parameters for pear ester, so the molecule can be identified in the broadband rotational spectrum, will also be described.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen which infects more than 50,000 people each year in the United States alone. Its abilities to move, colonize surfaces, and develop biofilms give rise to the high resistance to antimicrobial treatment. One type of motility employed by P. aeruginosa is swarming motility, where bacterial cells undergo physical and metabolic alterations. Swarming has been studied by many researchers but the knowledge on its chemical composition that relates to the transition between the motile and sessile biofilm stages are still lack. Here we apply confocal Raman microscopy (CRM) to examine P. aeruginosa wild-type PA14 (a virulent strain isolated from a burn wound) under swarming and biofilm conditions. The comparison between the swarming and biofilm samples indicates different molecules linked to the motile to sessile transition, revealing their community-specific chemical features. While the Pseudomonas quinolone signal (PQS) is found in swarm colonies and biofilms, the N-oxide quinolines (4-hydroxy-2-heptylquinoline-N-oxide,2-nonyl-4-hydroxyquinoline, etc.) are present in higher abundance and are synthesized and secreted much earlier in swarm colonies. Moreover, a closer investigation spanning from the center to the edge of a swarm colony shows high abundance of PQS at the center while N-oxides dominate the edge of the colony. The results provide insights into the chemical profile change occurring during the motile to sessile transition in P. aeruginosa, and demonstrate the broad application of CRM in biomolecular imaging. r0pt Figure

At present the road surface condition in the UK is monitored visually for any defects. This system works well to identify any major issues; however there is a very short window of time between detecting the defects and the complete failure of the surface. The road then requires resurfacing. It is therefore of interest to be able to predict the failure of the road surface in order to ensure the success of rejuvenation techniques. Asphalt road surfaces are constructed with three main components. Bitumen, a semi-solid, hydrocarbon based tar-like substance; fine filler, commonly calcium carbonate which adds bulk to the bitumen and stone based aggregates. There are many different mechanisms for the degradation of the road surfaces that involve chemical and physical factors. The chemical oxidation of bitumen is a contributing factor to the ageing of the asphalt road surfaces. The increase in oxygen levels within the composition and the loss of the lower molecular weight volatile components increases the polarity of the bitumen and leads to an increase in stiffness. As the bitumen becomes more brittle it loses its cohesion and adhesion with the aggregates and the surface begins to deteriorate. Bitumen oxidation can be monitored with the use of FTIR spectroscopy. The evolution of oxidation product functional group absorbance bands, including carbonyl, carboxylic and sulphoxide bonds can be monitored. This phenomenon has been well documented for raw bitumen but is less well understood for real road surfaces. This work investigates the use of diffuse reflectance IR spectroscopy, a non-contact measurement, to monitor the oxidation of bitumen and asphalt and relate this to pavement degradation. A number of different bitumen and asphalt samples have been aged naturally and artificially. Reflectance spectra have been collected alongside standardised mechanical testing of the physical properties of the bitumen in order to determine a link between the chemical and physical degradation. Preliminary results from this work identify the presence of oxidation product absorbance bands in the reflectance spectra as a result of ageing alongside a decrease in mechanical cohesion and an increase in stiffness and viscosity at lower temperatures.