Mid UV Research Articles

The Distribution of Iron over the Surface of 21 Com

Abstract Comparison of high dispersion LWP spectra obtained in 24 hr of monitoring of 21 Com with IUE in April 1991 reveals variations of low excitation Fe ii lines at phase 0.65 of the rotational period (FUV minimum flux) compared to phase 0.18 (FUV maximum flux). All 10 Fe ii lines of UV Multiplets 1 and 62 are consistently stronger at phase 0.65, which shows that the FUV flux minimum can be partially explained to an increase of the disk averaged iron abundance. In contrast, comparison of optical high resolution high signal-to-noise ELODIE spectra of 21 Com taken in 2004 April and separated by about half of the 2 days rotational period, reveals no significant variations of the Fe ii and Fe i lines. The lines monitored in the mid UV are strong low-lying transitions which are probably more sensitive to small abundance gradients over the surface of 21 Com.

A comparison of data quality using quartz vs. sapphire cell windows in analytical ultracentrifugation

Analytical ultracentrifugation (AUC) cells use either quartz or sapphire windows as end caps for the cell housing. Current generation sapphire windows are not recommended for absorbance data collection below 235nm, because the window material shows a precipitous drop in transmittance at low wavelengths due to impurities in the sapphire. Quartz windows can be used below 235nm as they do not exhibit adverse transmittance at low wavelengths. In this study, we demonstrate the optical properties of new generation sapphire windows and compare them to those of quartz windows across a wide range of wavelengths and present the results of sedimentation velocity experiments on BSA using both types of windows using data collected at both the 280nm absorbance maxima as well as the 230-240nm (closer to the peptide bond maximum). Our results show that the quartz and new generation sapphire windows deliver identical results in absorbance mode. We also demonstrate that quartz windows suffer significant mechanical deformation while spinning at very high speeds, while sapphire windows do not. This renders Rayleigh interference mode data collected at high speeds using quartz windows much noisier than with sapphire windows-which we have quantified by measuring how the signal to noise ratio of Fourier transformed Rayleigh interference scans degrades at high speed. Thus, we conclude that new-generation sapphire windows can be used for all AUC experiments through almost the entire mid UV range-obviating the need for quartz windows, unless wavelengths below 220nm must be accessed.

The Photocatalytic Degradation of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin in the Presence of Silver–Titanium Based Catalysts

Polychlorinated dibenzo-p-dioxins (PCDD) are persistent toxic compounds that are ubiquitous in the environment. The photodegradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the presence of silver titanium oxide (AgTi) and silver titanium doped into the Y-zeolite (AgTiY) was tested using high (254 nm) and mid (302 nm) energy UV irradiation sources. AgTi and AgTiY, both showed success in the photodegradation of 2,3,7,8-TCDD dissolved in methanol/tetrahydrofuran solution. Both catalysts were found to effectively decompose TCDD at 302 nm (lower energy) reaching in between 98–99% degradation after five hours, but AgTiY showed better performance than AgTi at 60 min reaching 91% removal. Byproducts of degradation were evaluated using Gas chromatography/mass spectrometry (GC–MS), resulting in 2,3,7-trichlorodibenzo-p-dioxin, a lower chlorinated congener and less toxic, as the main degradation product. Enzyme Linked Immunosorbent Assay (ELISA) was used to evaluate the relative toxicity of the degradation byproducts were a decrease in optical density indicated that some products of degradation could be potentially more toxic than the parent TCDD. On the other hand, a decrease in toxicity was observed for the samples with the highest 2,3,7,8-TCDD degradation, confirming that AgTiY irradiated at 302 nm is an excellent choice for degrading TCDD. This is the first study to report on the efficiency of silver titanium doped zeolites for the removal of toxic organic contaminants such as dioxins and furans from aquatic ecosystems.

Optical Applications of Nickel Sulphate Crystals at Elevated Temperature: A Characterization Study with the Addition of Amino Acid as an Impurity

L alanine added nickel sulphate hexahydrate (LANSH)crystals were grown by slow evaporation method in aqueous solution at room temperature. The grown crystals were characterized structurally, optically and thermally. X-ray diffraction studies proved the crystalline nature of the grown compound and it belongs to monoclinic structure. The presence of various functional groups was identified through FTIR analysis. The LANSH crystals are highly transparent in the mid UV wavelength range and hence these may be used in UV filters.In addition, thermo gravimetric analysis shows that the crystal is stable up to 110 °C. Therefore, LANSH can be employed in UV filters with higher ambient temperature too.

Mid-UV studies of the transitional millisecond pulsars XSS J12270−4859 and PSR J1023+0038 during their radio pulsar states★

We report mid-UV (MUV) observations taken with HST/WFC3, Swift/UVOT and GALEX/NUV of the transitional millisecond pulsars XSS J12270-4859 and PSR J1023+0038 during their radio pulsar states. Both systems were detected in our images and showed MUV variability. At similar orbital phases, the MUV luminosities of both pulsars are comparable. This suggests that the emission processes involved in both objects are similar. We estimated limits on the mass ratio, companion's temperature, inclination, and distance to XSS J12270-4859 by using a Markov Chain Monte Carlo algorithm to fit published folded optical light curves. Using the resulting parameters, we modeled MUV light curves in our HST filters. The resulting models failed to fit our MUV observations. Fixing the mass ratio of XSS J12270-4859 to the value reported in other studies, we obtained a distance of ~3.2 kpc. This is larger than the one derived from radio measurements (~1.4 kpc). Assuming a uniform prior for the mass ratio, the distance is similar to that from radio measurements. However, it requires an undermassive companion (~0.01 M_sun). We conclude that a direct heating model alone can not fully explain the observations in optical and MUV. Therefore, an additional radiation source is needed. The source could be an intrabinary shock which contributes to the MUV flux and likely to the optical one as well. During the radio pulsar state, the MUV orbital variations of PSR J1023+0038 detected with GALEX, suggests the presence of an asymmetric intrabinary shock.

Influence of temperature on thymine-to-solvent vibrational energy transfer

At the instant following the non-radiative deactivation of its ππ* electronic state, the vibrational modes of thymine possess a highly non-equilibrium distribution of excitation quanta (i.e., >4 eV in excess energy). Equilibrium is re-established through rapid (5 ps) vibrational energy transfer to the surrounding solvent. The mechanisms behind such vibrational cooling (VC) processes are examined here using femtosecond transient grating and two-dimensional photon echo spectroscopies conducted at 100 K and 300 K in a mixture of methanol and water. Remarkably, we find that this variation in temperature has essentially no impact on the VC kinetics. Together the experiments and a theoretical model suggest three possible mechanisms consistent with this behavior: (i) vibrational energy transfer from the solute to solvent initiates (directly) in intramolecular modes of the solute with frequencies >300 cm(-1); (ii) the relaxation induced increase in the temperature of the environment reduces the sensitivity of VC to the temperature of the equilibrium system; (iii) the time scale of solvent motion approaches 0.1 ps even at 100 K. Mechanism (i) deserves strong consideration because it is consistent with the conclusions drawn in earlier studies of isotope effects on VC in hydrogen bonding solvents. Our model calculations suggest that mechanism (ii) also plays a significant role under the present experimental conditions. Mechanism (iii) is ruled out on the basis of long-lived correlations evident in the photon echo line shapes at 100 K. These insights into photoinduced relaxation processes in thymine are made possible by our recent extension of interferometric transient grating and photon echo spectroscopies to the mid UV spectral region.

Comparison of four advanced oxidation processes for the removal of naphthenic acids from model oil sands process water

Four advanced oxidation processes (UV/TiO 2, UV/IO 4 −, UV/S 2O 8 2−, and UV/H 2O 2) were tested for their ability to mineralize naphthenic acids to inorganic carbon in a model oil sands process water containing high dissolved and suspended solids at pH values ranging from 8 to 12. A medium pressure mercury (Hg) lamp was used, and a Quartz immersion well surrounded the lamp. The treatment goal of 5 mg/L naphthenic acids (3.4 mg/L total organic carbon (TOC)) was achieved under four conditions: UV/S 2O 8 2− (20 mM) at pH 8 and 10, and UV/H 2O 2 (50 mM) at pH 8 (all with the Quartz immersion well). Values of electrical energy required to meet the treatment goal were about equal for UV/S 2O 8 2− (20 mM) and UV/H 2O 2 (50 mM) at pH 8, but three to four times larger for treatment by UV/S 2O 8 2− (20 mM) at pH 10. The treatment goal was also achieved using UV/S 2O 8 2− (20 mM) at pH 10 when using a Vycor filter that transmits light primarily in the mid and near UV, suggesting that that treatment of naphthenic acids by UV/S 2O 8 2− using low pressure Hg lamps may be feasible.

Processing of Lithographically Defined Apex Glass Structures with Smooth and Transparent Sidewalls

We demonstrate a process to improve the surface roughness and optical transparency of the sidewalls of structures made in ApexTM photosensitive glass. Improved sidewall roughness is achieved through a post- etch anneal that reflows the surface of the glass microstructure and reduces the size of roughened glass nodules on the HF etched surface. The same anneal process is equally suited for bonding between substrates as the surface of the glass is melted allowing the glass to reflow across the seam of the bond. The process involves four basic steps: the glass sample is exposed to mid UV light to photo-activate metallic particles, followed by a two-stage baking process to allow for formation of metallic nanoclusters in the glass matrix. The amorphous glass is then etched in a diluted 3–4% (by volume) HF solution. Finally the glass structure undergoes a post-etch annealing processes at 630°C for 15 min to smoothen the etched surface and enhance the transparency of the glass sidewalls. The surface roughness obtained was approximately 200  36 nm. The surface roughness prior to post etch annealing was over 1 μm with a standard deviation of 0.4 μm. Thermal loading was observed between structures of varying size at these temperatures. The improvement of transparency in the sidewalls renders the glass structures useful for micro-optical sensors. Future work will investigate the use of this process for the development of visible and near IR microspectrometer curvets.

ETA CARINAE ACROSS THE 2003.5 MINIMUM: ANALYSIS IN THE VISIBLE AND NEAR-INFRARED SPECTRAL REGION

We present an analysis of the visible through near infrared spectrum of Carinae and its ejecta obtained during the Eta Carinae Campaign with the UVES at the ESO VLT. This is a part of larger effort to present a complete Carinae spectrum, and extends the previously presented analyses with the HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near UV is characterized by the ejecta absorption. At longer wavelengths, stellar wind features from the central source and narrow emission lines from the Weigelt condensations dominate the spectrum. However, narrow absorption lines from the circumstellar shells are present. This paper provides a description of the spectrum between 3060 and 10,430 A, including line identifications of the ejecta absorption spectrum, the emission spectrum from the Weigelt condensations and the P-Cygni stellar wind features. The high spectral resolving power of VLT/UVES enables equivalent width measurements of atomic and molecular absorption lines for elements with no transitions at the shorter wavelengths. However, the ground based seeing and contributions of nebular scattered radiation prevent direct comparison of measured equivalent widths in the VLT/UVES and HST/STIS spectra. Fortunately, HST/STIS and VLT/UVES have a small overlap in wavelength coverage which allows us to compare and adjust for the difference in scattered radiation entering the instruments' apertures. This paper provides a complete online VLT/UVES spectrum with line identifications and a spectral comparison between HST/STIS and VLT/UVES between 3060 and 3160 A.

A chromospheric scenario for the activity ofβ Pictoris, as revealed by FUSE

We investigate a chromospheric scenario to explain the characteristics of the far-UV emission lines of Pictoris, revealed by FUSE spectra of this famous circumstellar disk system. The model assumes a thin region heated up to a few 10 5 K located close to the stellar photosphere. The resonance lines of C III at 977 A and O VI at 1032-1037 A, seen in emission, are produced in this chromosphere-transition region complex. Using complementary data in the mid and near UV (specifically, a resonance doublet of C IV at 1548-1550 A and Mg II h & k), we show that the whole dataset is remarquably well reproduced by the model. In addition, we investigate the properties of the C III* multiplet at 1176 A and conclude that this line likely forms in a weak warm wind, originating from the prominent circumstellar disk of Pictoris. Finally, radiative losses have been calculated and have provided estimates of the amount of non radiative energy dissipated in the external atmosphere of Pictoris, which is a measure of the star's activity level. Such behavior for an A5 V star presents a challenge for both evolution and activity models since the former predict that main-sequence A stars should not be active, while the latter are unable to quantitatively account for the characteristics of the chromospheric heating of Pictoris.

The temperature dependent absorption cross sections of C 4H 2 at mid ultraviolet wavelengths

We have measured the mid UV (195–265 nm) absorption coefficients of diacetylene, C 4H 2, over the temperature range 193–293 K. An impurity involved in the synthesis of C 4H 2, namely C 4H 3Cl, can strongly influence the measured absorption coefficients. This impurity has a mid UV absorption approximately 300 times stronger than C 4H 2 and we demonstrate that its presence, at low levels, in previously published spectra has strongly influenced the published coefficients and their temperature dependence. We have obtained an ultra-pure sample of C 4H 2 by repeated distillation and show here its clean spectrum and temperature dependence. We confirm previous band assignments, but our superior resolution (0.02 nm) has shown the presence of other, previously undetected bands. These new results have wide implications for the modelling of Titans atmosphere and the analysis of observational data.

Laser induced chemical and physical modifications of polymer films: dependence on the irradiation wavelength

Polymers with photolabile groups absorbing in the mid UV (around 300 nm) were irradiated with excimer-lasers (248 and 308 nm). Irradiation with 248 nm (KrF laser) corresponds to an excitation of the photostable phenyl system whereas the XeCl laser (308 nm) excites the labile triazeno groups (–NN–N). Thin polymer films (0.1–3 μm) were coated onto quartz or glass and irradiated below and above the threshold of ablation. The films were subsequently analyzed with various surface analysis techniques. Below the threshold of ablation the main feature at both irradiation wavelengths was the reduction of the absorption maximum at about 330 nm and an increase of the surface oxygen content (X-ray photoelectron spectroscopy) and therefore the surface polarity (contact angle). The surface remained smooth with no detectable micro-structures (scanning electron microscopy). Above the ablation threshold the absorbance at 330 nm decreased dramatically and the color of the film changed. For 248 nm irradiation the surface was darkened and a carbonization (XPS) with microstructures (SEM) was detected. The surface became non-polar in agreement with surface carbonization. In the case of 308 nm irradiation the surface remained smooth and no change of the chemical composition or surface polarity was detected, suggesting a photochemically induced layer by layer ablation process.

Contribution to interstellar extinction from an astrophysical microsoot?

The optical constants of a carbon polymorph, calculated using the Drude dispersion theory, are shown to lead to close agreements with the mean interstellar extinction curve over the waveband 0.3 ≤ λ-1 ≤ 5.5 μm-1 for particles of Rayleigh scattering sizes. Astrophysical microsoot grains of radii ≤50A may be related to microdiamond grains of similar sizes that have recently been discovered in carbonaceous chondrites. It is postulated that such microsoot particles could contribute to the nearly invariable interstellar extinction law observed over the near IR, visible and near to mid UV spectral regions. Admixtures of microsoot with micron-sized microsoot clumps, microdiamond and hollow organic / biologic grains provide an explanation for the full range of extinction and polarization data.

UV Characteristics and Performance as Positive-Working Deep, Mid, and Near UV Resists of Phenyl Isopropenyl Ketone Copolymers

UV Characteristics and Performance as Positive-Working Deep, Mid, and Near UV Resists of Phenyl Isopropenyl Ketone Copolymers

Chloromethylated Poly(naphthyl methacrylate) as Electron Beam and Photo Resist

Resists applicable to both electron beam and mid UV (300—400 nm) photolithographies were designed, and chloromethylated poly(naphthyl methacrylates) (CMN) were synthesized. The sensitivity of CMN with Mw of 1.4×105, which resolved 0.5 μm of line and space was 4.5μC cm−2. CMN could be used as photo-resist by the addition of suitable photo-sensitizer such as Michler’s ketone. CMN with 3wt% Michler’s ketone showed high sensitivity (D0.5=100 mJ cm−2) and resolved 2μm minimum line.

Dosimetry for lithographic applications

Because of the demand for miniaturization of devices, lithographic tools are becoming more expensive and sophisticated with future emphasis being placed on x rays, e beams, and ultraviolets in the range of 2200–3200 Å. It is increasingly important to be able to easily monitor exposure dose and uniformity from tool to tool in an industrial environment. This paper investigates the use of commercially available dosimeter films for lithography applications. These films consist of radiachromic dye derivatives in various polymers. Upon exposure to ultraviolet light (<3400 Å) and other ionizing radiation, these films undergo photoionization, and change from a colorless to a deeply colored state as a direct function of the radiation exposure received. Therefore, the optical density is a means of measuring the amount of incident radiation. For e-beam dosimetry, a measurable optical density change is observed between 0.1 and 20 μC/cm2 with saturation occurring at ∠25 μC/cm2. Maximum penetration range of the 25-kV beam was determined to be 20–25 μ. For x-ray application, the film is similar to e-beam, with a linear response up to 100 mJ/cm2 using the Al–Kα line. For mid UV at 3130 Å and deep UV at 2200 Å, the dosimeter is very sensitive with a 5% change in transmission occurring for every 1 mJ/cm2 dose variation.

Quasi-simultaneous observations of BL Lac object MRK 501 in X-ray, UV, visible, IR, and radio frequencies

Quasi-simultaneous observations of the BL Lacertae (Lac) objects MK 501 were performed for the first time at X-ray, ultraviolet, visible, infrared, and radio frequencies. The observed spectral slope from the X-ray to UV regions is positive and continuous, but that from the mid UV to visible light region becomes gradually flat and possibly turns down toward lower frequencies; the optical radio emission can not be accounted for by a single power law. Several theoretical models were considered for the emission mechanism. A quantitative comparison was performed with the synchrotron-self-Compton model; the total spectrum is found consistent with this model. The spectrum from visible light to X-ray is consistent with synchrotron radiation or with inverse-Compton scattering by a hot thermal cloud of electrons. The continuity of the spectral slope from X-ray to UV implied by the current data suggests that the previous estimates of the total luminosity of this BL Lac object is underestimated by a factor of about three or four.