OH Absorption Spectra Research Articles

The influence of the volume concentration of hydrogen on the fine structure of the IR absorption spectra and conductivity features in congruent LiTaO3 crystals

A new method for changing the volume concentration of hydrogen in congruent LiTaO3 (lithium tantalate, LT) crystals has been studied. It has been established that pre-treatment of the sample in adipic acid significantly increases the volumetric concentration of hydrogen in the sample during subsequent annealing in a humid atmosphere at a relatively low annealing temperature. First of all, this preserves the LT single crystal in a single-domain state. In contrast to known methods for increasing the volumetric concentration of hydrogen, the proposed method affects the absorption coefficient of the sample in the optical range less than for a congruent LiNbO3 crystal. It has been shown that the type of IR absorption spectrum of OH− groups and the defect structure of the LT crystal significantly depend on the volume concentration of hydrogen in the sample. The study also analyzed the reasons for this effect. The temperature dependences of the electrical conductivity of LT samples with different hydrogen concentrations have been studied. It has been shown that the type of electronic conductivity of LT samples changes when the concentration of OH groups in the crystal increases significantly.

Synchronic measurements of temperatures and concentrations of OH, NH, and NO in flames based on broadband ultraviolet absorption spectroscopy

Temperature is an important parameter influencing the combustion reaction path and rate and determining the combustion and energy exchange efficiency. The OH, NH, NO and other species are involved in the key elementary reactions of combustion and determine the generation of NO<i><sub>x</sub></i> pollutants. Therefore, temperature and concentration measurements of OH, NH, and NO are of great significance for combustion diagnostics and research on reaction or emission mechanisms. In this work, a measurement system with high spatial resolution based on broadband ultraviolet absorption spectroscopy is established to realize simultaneous measurements of the temperature and concentrations of OH, NH, and NO in flames. Low detection limits of these three species are achieved by using the established measurement method. The 1<i>σ</i> detection limit of NH is 1.8 ppb·m (1560 K), which is realized for the first time in atmospheric-pressure flames using absorption spectroscopy. The 1<i>σ</i> detection limits of OH and NO are 60 ppb·m (1590 K) and 1 ppm·m (1380 K), respectively, which are obviously better than the existing results obtained by using infrared laser absorption spectroscopy. Then, the distributions of temperatures and concentrations of OH, NO and NH are acquired at various heights in an atmospheric-pressure NH<sub>3</sub>/CH<sub>4</sub>/air premixed flat flame with a high spatial resolution of nearly 0.1 mm. The broadband absorption spectra of OH and NH are acquired simultaneously inside the flame front, and the spectra of OH and NO are acquired simultaneously above the flame front. Inside or near the flame front, the temperatures deduced from the spectra of OH, NH, and NO are consistent, verifying the ability of these three species to be used to measure temperature. In addition, OH, NH, and NO are found to be suitable for different regions in combustion. The OH absorption is suitable for the post-combustion region with temperatures higher than 1000 K, the NH absorption can be used to acquire the temperature inside the flame front in complex combustion, and the NO absorption was able to provide the temperature in the region before or outside combustion at lower temperatures. Additionally, the experimental temperature and concentration profiles are in good agreement with the computational fluid dynamics predictions based on the mechanism, exhibiting the accuracy of the simultaneous temperature and concentration measurements by using broadband ultraviolet absorption spectra. Moreover, the differences in temperature and OH concentration between experiments and simulations indicate that the carbon sub-mechanism in the mechanism given by Okafor et al. [Okafor E C, Naito Y, Colson S, Ichikawa A, Kudo T, Hayakawa A, Kobayashi H <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1016/j.combustflame.2017.09.002">2018 <i>Combust. Flame</i> <b>187</b> 185</ext-link>] should be further improved for more accurate predictions of NH<sub>3</sub>/CH<sub>4</sub> combustion.

Experimental study of water solubility in iron rich olivine

地幔的力学性质主要受橄榄石流变性的控制，含水对橄榄石流变性质的影响很大，而橄榄石的水溶性受到温度和铁含量的影响，因此，本文进行了不同铁含量橄榄石在不同温度下的水溶性实验研究。实验使用的样品为天然橄榄石单晶Fa₁₇和Fa_24.7（Fe_No.=100×molar Fe/（Mg+Fe））以及人工合成的橄榄石单晶Fa₂₂；橄榄石单晶的水溶性实验在300MPa围压和1273~1473K的温度条件下进行，每隔50K进行一组实验，氧逸度被控制在NiNiO水平上。实验结束后，对橄榄石单晶沿b面进行双面研磨抛光，用电子探针分析确定橄榄石单晶成分，采用EBSD精确测量橄榄石的单晶方向，使用红外光谱仪（FTIR）的非偏振光路测试橄榄石单晶在b轴上的吸收光谱。对FTIR吸收光谱进行积分得到富铁橄榄石的水溶性实验结果:当温度由1273K升至1473K时，橄榄石单晶Fa₁₇的水溶性变化为600~1200H/10⁶ Si，橄榄石单晶Fa_24.7的水溶性变化为1000~1300H/10⁶ Si，人工合成的橄榄石单晶Fa₂₂的水溶性变化为500~900 H/10⁶ Si。因此，相同铁含量橄榄石单晶的水溶性随温度的增加而增加，相同温度条件下，天然形成的橄榄石的水溶性随着铁含量的增加而增加，百分之一的铁含量的增加，可以导致约百分之十的水溶性的增加。本文所研究的不同铁含量的橄榄石可以为更好地估算上地幔水溶性提供依据。;The mechanical property of the upper mantle is controlled by the rheological properties of olivine. Water has great influence on the mechanical properties of olivine. Results showed that different temperatures and iron contents have influence on the water solubility of olivine. Therefore, the water solubility experiment was conducted on olivine with different iron contents at different temperatures in this paper. The olivine single crystals used in this study include natural San Carlo olivine single crystal Fa₁₇, Fa_24.7(Fe_no.=100×molar Fe/(Mg+Fe))and synthetic olivine single crystal Fa₂₂. Experiments were performed at temperatures between 1273K and 1473K with 50K increments at a confining pressure of 300MPa in a gas medium apparatus with oxygen fugacity buffered by the Ni:NiO. After the test, the olivine single crystal was double polished along b-plane. The composition was measured by Electron Probe, the orientation was determined by Electron Backscattered Diffraction (EBSD) and the OH absorption spectra were recorded by infrared spectroscopy, respectively, for each of the single crystal. Results showed that, when the temperature changes from 1273K to 1473K, the water solubility of Fa₁₇olivine varied from 600 to 1200 H/10⁶ Si, Fa₁₇ olivine from 1000 to 1300 H/10⁶ Si and the synthetic Fa₂₂olivine from 500 to 900 H/10⁶ Si, respectively. Therefore, the water solubility of the olivine with the same iron content increases with the increase of the temperature. The water solubility of the olivine at the same temperature increases with the increase of the iron content for natural San Carlo olivine. One percent increase in iron content resulted in ten percent increase in water solubility. In this paper, the water solubility in olivine at several Fe contents can be used to estimate the water storage in the upper mantle.

Effects of temperature and pressure on OH laser-induced fluorescence exciting A–X (1,0) transition at high pressures**Project supported by the National Natural Science Foundation of China (Grant Nos. 51976233 and 91641118).

The effects of temperature and pressure on laser-induced fluorescence (LIF) of OH are numerically studied under the excitation of A–X (1,0) transition at high pressures. A detailed theoretical analysis is carried out to reveal the physical processes of LIF. It is shown that high pressure LIF measurements get greatly complicated by the variations of pressure- and temperature-dependent parameters, such as Boltzmann fraction, absorption lineshape broadening, central-frequency shifting, and collisional quenching. Operations at high pressures require a careful choice of an excitation line, and the Q1(8) line in the A–X (1,0) band of OH is selected due to its minimum temperature dependence through the calculation of Boltzmann fraction. The absorption spectra of OH become much broader as pressure increases, leading to a smaller overlap integral and thus smaller excitation efficiency. The central-frequency shifting cannot be omitted at high pressures, and should be taken into account when setting the excitation frequency. The fluorescence yield is estimated based on the LASKIN calculation. Finally, OH-LIF measurements were conducted on flat stoichiometric CH4/air flames at high pressures. And both the numerical and experimental results illustrate that the pressure dependence of fluorescence yield is dominated, and the fluorescence yield is approximately inversely proportional to pressure. These results illustrate the physical processes of OH-LIF and provide useful guidelines for high-pressure application of OH-LIF.

Excited states of OH-(H₂O)n clusters for n = 1-4: an ab initio study.

Equation of motion coupled cluster calculations were performed on various structures of OH in clusters with one, two, three, and four water molecules to determine the energies of valence and charge transfer states. Motivation for these calculations is to understand the absorption spectrum of OH in water. Previous calculations on these species have confirmed that the longer wavelength transition observed is due to the A((2)∑) ← X((2)∏) valence transition, while the shorter wavelength transition is due to a charge-transfer from H2O to OH. While these previous calculations identified the lowest energy charge-transfer state, our calculations have included sufficient states to identify additional solvent-to-solute charge transfer states. The minimum energy structures of the clusters were determined by application of the Monte Carlo technique to identify candidate cluster structures, followed by optimization at the level of second-order Møller-Plesset perturbation theory. Calculations were performed on two structures of OH-H2O, three structures of OH-(H2O)2, four structures of OH-(H2O)3, and seven structures of OH-(H2O)4. Confirming previous calculations, as the number of water molecules increases, the energies of the excited valence and charge-transfer states decrease; however, the total number of charge-transfer states increases with the number of water molecules, suggesting that in the limit of OH in liquid water, the charge-transfer states form a band.

Dynamics of water state in nanoconfined environment

To investigate water state in vitro conditions, cetyltrimethylammonium bromide/isooctane 1-hexanol reverse micellar system was used as a model for nanoscale medium. Using Fourier transform infrared spectroscopy and deconvolution technique, the water states in these systems were studied at several water/surfactant molar ratios, wo, with respect to time. The presence of four sub-peaks in deconvolution of FT-IR absorption spectra of OH stretching band certified four different states of water. The results showed time dependency of water state, especially in those systems having low wo, that are more dynamic. Also, exchange of water molecules between different states results in approaching each state to a final steady state value. Based on deconvolution results, it was found that mechanism of ionizing surfactant head group can control water bonded to the bromide counter ion. Moreover, more than 50% of water molecules are like frozen water in reverse micelles and they are not available for solubilization of hydrophilic compounds. Based on the results of this study, state and properties of water in nanoscale medium are quite different from bulk scale.

OH-defects in Al- and Cr- doped synthetic enstatites and defect geobarometry on natural orthopyroxenes from the Earth's mantle

Hydrogen incorporation mechanisms in synthetic enstatite (Mg 2 Si 2 O 6 ), doped with Al or Cr and Al and Cr, and coexisting with forsterite were studied experimentally at 4–8 GPa at 1150 °C. The IR spectra show two different groups of OH-absorption bands: group 1 (wavenumbers between 3500 and 3730 cm −1 ) and group 2 (wavenumbers between 2800 and 3500 cm −1 ). The intensity ratio of group 2 to group 1 bands ( e.g. , ( A 3362 )/( A 3692 )) is sensitive to pressure and to the Al/Cr ratio incorporated in enstatite. In addition, for samples doped with Al and Cr, the OH content is not a simple function of Al and Cr, suggesting OH-defect annihilation if both trivalent cations are present. Modelling of OH-incorporation into enstatite suggests that the water storage capacity in mantle orthopyroxene under average conditions of a continental geotherm is higher than in pure enstatite, but much lower than simple substitution mechanisms would suggest. Based on the observed pressure trend in the OH-absorption spectra of the synthetic samples, IR spectra of eleven natural samples were evaluated. Even if synthetic and natural samples do not show the same trend, a pressure trend for the natural samples could be established, and a geobarometer for the OH-characteristics of natural orthoenstatite from the Earth’s mantle (coexisting with forsterite) can be formulated as P [ GPa ] = 63.4 · A ( 3487 - 3240 ) + A ( 3570 - 3487 ) A ( 3487 - 3240 ) + A ( 3570 - 3487 ) + A ( 3730 - 3570 ) - 48.8 , where A ( a–b ) is the integral absorbance of the component E||n γ + E||n β of the absorption bands between a cm −1 and b cm −1 , respectively.

Evolution characteristic of OH absorption in Mg (5 mol% in melt):LiNbO3 crystal with post-grown Li-poor vapor transport equilibration

We have measured OH absorption spectra of a 0.47-mm-thick Z-cut MgO (5mol% in melt):LiNbO3 crystal subjected to post-growth Li-poor vapor transport equilibration (VTE) treatments at 1100°C for different durations ranging from zero to 395h. These spectra allow the evolution of OH absorption characteristics with prolonged VTE to be followed. After 2h of VTE process an additional absorption appears at 3483cm−1. A transition regime that the original 3536cm−1 and new 3483cm−1 absorptions simultaneously appear exists within the VTE duration range of 2–16h. In this regime, the 3536cm−1 absorption becomes weak gradually and eventually disappears around 16h while the 3483cm−1 absorption increases remarkably with the prolonged VTE. The presence of transition regime gives a hint that the 3483cm−1 absorption is due to the VTE-induced formation of a new center. Based upon the spectral features, we have suggested a simple three-layer (two on surface and one in the center of crystal plate) model to describe the depth profile of the photorefractive damage MgO concentration threshold in the crystal in the transition regime. A Li out-diffusion theory is suggested and correlated with the model. To support the Li out-diffusion theory, some additional experiments have been done. These include the depth profile characterization of VTE-induced Li2O content reduction and the measurement of the surface Li2O content as a function of the VTE duration. A quantitative analysis and discussion shows that the model is well supported by the experimental results.

Influence of MgO codoping on Er concentration in congruent LiNbO3 crystal: Mg threshold concentration effect

Congruent Er:Mg:LiNbO3 crystals were grown by the Czochralski method from the melts containing fixed 0.5 mol% Er2O3 while varied MgO content ranged from 0.0 to 8.0 mol%. The Mg and Er contents in the crystals were determined by neutron activation analysis. In the presence of Er codopant, the Mg threshold concentration with respect to optical damage is determined from the measured OH absorption spectra. The results show that the Er codopant has less effect on both the Mg threshold concentration and Mg segregation coefficient, which is within 1.13–1.23 as the Mg concentration is below the threshold while within 0.88–0.98 when above the threshold, consistent with the only MgO doping case. On the other hand, the practical Er concentration in the crystal is closely related to the Mg content and shows definite Mg threshold effect. Below the threshold, the Er concentration decreases linearly with the increased Mg concentration in the crystal; above the threshold, the decrease is more remarkable and follows another linear function. The Mg concentration effect on the Er segregation coefficient is discussed from the viewpoint of the Mg doping effect on the solubility of Er ions in the crystal.

Molecular Structure and UV Absorption Spectra of OH and NH2 Derivatives of Dodecamethylcyclohexasilane: A Combined Experimental and Computational Study

The monofunctionalized cyclohexasilanes XSi6Me11 [X = -OH (2); -NH2 (3)] are easily accessible from XSi6Me11 and H2O/Et3N or NH3, respectively. The crystal structure of 2 as determined by single crystal X-ray crystallography exhibits the cyclohexasilane ring in chair conformation with the OH group in an unusual equatorial position due to intermolecular hydrogen bonding. Full geometry optimization (B3LYP/6-31+G∗) of the gas-phase structures of 2 and 3 affords six minima on the potential energy surface for chair, twist and boat conformers with the heterosubstituents either in axial or equatorial positions all being very close in energy. According to time-dependent DFT B3LYP/TZVP calculations contributions of several conformers to the observed solution UV absorption spectra of dodecamethylcyclohexasilane (1), 2 and 3 need to be considered in order to achieve satisfactory agreement of calculated and experimental data

Calibration of the infrared molar absorption coefficients for H in olivine, clinopyroxene and rhyolitic glass by elastic recoil detection analysis

We use a nuclear microbeam technique (Elastic Recoil Detection Analysis or ERDA) to measure the H content in 2 rhyolitic glasses, 4 olivines, 4 orthopyroxenes, and 7 clinopyroxenes. These samples have been characterized previously for their OH absorption spectra by infrared (FTIR) spectroscopy. We use ERDA and FTIR data to calibrate the infrared molar absorption coefficients. The blank level of the ERDA method is 102 ± 81 ppm H 2O, too great for the analysis of many natural nominally anhydrous minerals (NAMs) from the upper mantle, but applicable to H-rich glasses, natural and synthetic NAMs. Calibration of the molar absorption coefficient ε with the ERDA results gives 95 ± 8 l mol − 1 cm − 1 for rhyolitic glasses (peak height), 34,515 ± 7050 l mol − 1 cm − 2 for olivine and 46,103 ± 5300 l mol − 1 cm − 2 for clinopyroxene (integrated area). The olivine calibration of the present study is intermediate between that of Bell et al. [Bell, D.R., Rossman, G.R., Maldener, J., Endisch, D. and Rauch, F., 2003. Hydroxide in olivine: a quantitative determination of the absolute amount and calibration of the IR spectrum. Journal of Geophysical Research, 108(B2). doi:10.1029/2001JB000679] and that of Libowitzky and Rossman [Libowitzky, E. and Rossman, G.R., 1997. An IR absorption calibration for water in minerals. American Mineralogist, 82: 1111–1115]. For clinopyroxene, the best agreement with the ERDA data is obtained for the Libowitzky and Rossman [Libowitzky, E. and Rossman, G.R., 1997. An IR absorption calibration for water in minerals. American Mineralogist, 82: 1111–1115] calibration (5% lower than the ERDA data). The present calibration also confirms that the Paterson [Paterson, M.S., 1982. The determination of hydroxyl by infrared absorption in quartz, silicate glasses and similar materials. Bulletin de Mineralogie, 105: 20–29] calibration systematically underestimates the OH content in olivine.

OH absorption spectroscopy in a flame using spatial heterodyne spectroscopy

We demonstrate measurements of OH absorption spectra in the post-flame zone of a McKenna burner using spatial heterodyne spectroscopy (SHS). SHS permits high-resolution, high-throughput measurements. In this case the spectra span approximately 308-310 nm with a resolution of 0.03 nm, even though an extended source (extent of approximately 2x10(-7) m(2) rad(2)) was used. The high spectral resolution is important for interpreting spectra when multiple absorbers are present for inferring accurate gas temperatures from measured spectra and for monitoring weak absorbers. The present measurement paves the way for absorption spectroscopy by SHS in practical combustion devices, such as reciprocating and gas-turbine engines.

Signature OH Absorption Spectrum from Cluster Models of Solvation: A Solvent-to-Solute Charge Transfer State

Ab initio electronic structure theory calculations on cluster models support the characterization of the signature absorption spectrum of a solvated hydroxyl OH radical as a solvent-to-solute charge transfer state modulated by the hydrogen-bonding environment. Vertical excited states in OH(H2O)n clusters (n = 0-7, 16) calculated at the TDDFT level of theory (with companion calculations at the EOM-CCSD level of theory for n </= 7) show an intense band in the region of approximately 250 nm. The calculations suggest that the intensity of the solvent-to-solute charge transfer transition depends strongly on a favorable alignment of the donor and acceptor molecular orbitals, as observed in one (n = 16) cluster. In the other (smaller) clusters, the transitions in this region were found to be weak as the clusters do not offer the necessary favorable alignment of orbitals. The present findings are consistent with the experimentally observed absorption at 230 nm that has been assigned to a solvent-to-solute charge transfer and provide insight into the electronic states and orbitals that give rise to the intensity of the band.

Late‐Time Observations of the Afterglow and Environment of GRB 030329

We present Very Long Baseline Interferometry (VLBI) observations 217 days after the {gamma}-ray burst of 2003 March 29. These observations provide further measurements of the size and position of GRB 030329 that are used to constrain the expansion rate and proper motion of this nearby GRB. The expansion rate appears to be slowing down with time, favoring expansion into a constant density interstellar medium, rather than a circumstellar wind with an r{sup -2} density profile. We also present late time Arecibo observations of the redshifted Hi and OH absorption spectra towards GRB 030329. No absorption (or emission) is seen allowing us to place limits on the atomic neutral hydrogen of N{sub H} < 8.5 x 10{sup 20} cm{sup -2}, and molecular hydrogen of N{sub H{sub 2}} < 1.4 x 10{sup 22} cm{sup -2}. Finally, we present VLA limits on the radio polarization from the afterglow of <2% at late times.

PSR B1849+00 Probes the Tiny-Scale Molecular Gas?

In this paper we present and discuss the great difference in OH absorption spectra against PSR B1849+00 and SNR G33.6+0.1 along the same line-of-sight. This finding is important as it clearly demonstrates that statistics of absorbing molecular gas depends on the size of the background source.

Detection of OH and wide H i absorption toward B0218+357

We present deep GMRT OH and WSRT HI absorption spectra of the $z = 0.6846$ gravitational lens toward B0218+357. Both the 1665 MHz and 1667 MHz OH lines are clearly detected for the first time while a new wide absorption component was detected (at low significance) in the HI spectrum; the OH spectra yielded an OH column density of $N_{OH} = 2.3 \times 10^{15}$ cm^{-2}. The ratio of 1667 and 1665 MHz equivalent widths is $\sim 1.8$ while the redshift of peak OH absorption is $z = 0.68468 \pm 0.000008$ for both lines; this redshift agrees with that obtained from the HI line. The velocity spread (between nulls) of the HI absorption is $\sim 140$ km/s, while that of both OH lines is $\sim 100$ km/s; the HI and OH spectra are broadly similar in that they each have two principal narrow components and a wide absorption trough. We argue that the wide absorption is likely to arise from source components in the Einstein ring and derive a rotation velocity of $\sim 150$ km/s at a distance of 1.5 kpc from the centre of the $z \sim 0.6846$ galaxy.

In-situ Measurements of Tropospheric Hydroxyl Radicals by Folded Long-Path Laser Absorption During the Field Campaign POPCORN

Absolutely calibrated in-situ measurements of tropospheric hydroxyl radicals, formaldehyde, sulfur dioxide, and naphthalene (C10H8) were performed by long-path laser absorption spectroscopy during the field campaign POPCORN. The absorption light path was folded into an open optical multiple reflection cell with a mirror separation of 38.5 m. Using a light path length of 1848 m and an integration time of 200 s, the average 1σ-detection limits of OH, HCHO, SO2 and C10H8 during POPCORN were 8.7 · 105 cm−3, 8.3 · 109 cm−3, 2.4 · 109 cm−3, 1.5 · 108 cm−3, respectively. In total, 392 identifications of OH in air spectra were made in a rural environment between August 5 and August 23, 1994. We present and discuss OH absorption spectra and diurnal OH concentration profiles of three days which are representative for measurements under different pollution conditions during POPCORN. The observed maximum and median OH radical concentrations are 1.3 · 107 OH/cm3 and 4.0 · 106 OH/cm3, respectively. The measured diurnal variation of the OH concentration shows a good correlation with the primary formation reaction of OH radicals which is the photolysis of ambient ozone. Deviations from this correlation in the morning and evening hours, when the OH concentration is higher than expected from the ozone photolysis, demonstrate the importance of other photochemical HOx production pathways during POPCORN.

Chlorination reduction in sol—gel-derived porous silica gels

Chlorine dehydroxylation in plate-like silica gels prepared by hydrolysis of Si(OCH 3) 4 was investigated for gels treated in chlorine at 800°C. The infrared absorption spectrum of OH on the open pore surface of the gel was measured. The exchange reaction between OH and Cl was found to decrease linearly with the square root of treatment time and with reciprocal gel thickness. The dependence of the dehydroxylation rate on gel thickness indicated that the exchange between OH and Cl is limited by Cl 2 diffusion into the gel.

Origin and characteristics of internal fields in LiNbO3 crystals

We report the presence of an in-built internal field in Z-cut LiNbO3 crystals of 3.35KV/mm in the direction of the polarization in a virgin crystal. Upon polarization reversal under an electric field, the internal field tends to realign along the new polarization direction. At room temperature, this realignment process was incomplete even after many days, while on annealing at 250°C for 2 min followed by cooling down, ∼ 80% recovery was observed (from + 3.35 KV/mm to −2.14 KV/mm). A change in the infrared absorption spectrum of OH− ions in LiNbO3 crystal was also observed upon polarization reversal at room temperature. Upon annealing above 200°C for a few minutes followed by cooling to room temperature, the shape of the spectrum partially recovers to that of the virgin crystal at room temperature, indicating a strong correlation between OH− ions and internal field in LiNbO3 crystals. We also show that 180° domains in a polarization reversed LiNbO3 crystal can be observed by light microscope, suggesting structural changes in the regions close to domain walls.

PROPELLANT COMBUSTION DIAGNOSTICS VIA MULTICHANNEL ABSORPTION SPECTROSCOPY

Multichannel absorption spectroscopy has been developed and used to non-intrusively probe the hostile environment of solid propellant combustion. A windowed pressure vessel, broadband light source, and a spectrometer-array detector system are the major components of the experiment. Gas phase absorption spectra obtained during the steady-state combustion of double-base and nitramine propellants can be analyzed to determine temperature and absolute concentration profiles. The analysis requires only fundamental spectroscopic data incorporated into the differential absorption law. Ultraviolet-visible sensitive multichannel detectors have been used to obtain absorption spectra of NO, OH, NH, and CN during the combustion of solid propellants and their ingredients. Focus has been primarily on the propellant dark zone with simultaneous tracking capability for NO and OH. Vibrationally resolved transitions in the Α2Σ-Χ2Π electronic system of NO allow determination of temperature and absolute NO concentration. Rotationally resolved transitions in the Α2Σ-Χ2Π(0,0) vibrational band system of OH allow determination of OH concentration and luminous flame temperature. An infrared-sensitive multichannel detector has been used to obtain rotational-vibrational absorption spectra for CO, HCN, H2O, CO2, N2O, and CH4 in the dark-zone region. Substantial HCN concentrations occur in the dark zone of nitramine propellants, but not in the dark zone of double base propellants. Dark-zone temperatures derived from fitting the infrared absorption spectra of HCN and H2O are in good agreement with those obtained from fitting NO in the ultraviolet region. Concentrations of these infrared active species have been determined. Multichannel absorption spectroscopy, along with other experimental diagnostic techniques such as microprobe mass spectrometry, FT-IR spectroscopy and use of thermocouples, have greatly expanded the propellant database for quantitative gas-phase composition and temperature profiles. This information is presently being used to refine reduced reaction mechanisms for propellant dark-zone chemistry as well as to validate models of solid propellant combustion.