Marsel V. Zagidullin

Results of small-signal gain measurements on a supersonic chemical oxygen iodine laser with an advanced nozzle bank

High-resolution diode laser spectroscopy has been used to probe the gain in the active medium formed by an advanced supersonic chemical oxygen iodine laser (COIL), ejector nozzle bank. The probe beam was directed through the medium at 90/spl deg/ (normal) to the flow velocity and at an angle of 27.5/spl deg/ away from normal incidence. Analysis of the small-signal gain spectrum allowed for the determination of the gain, average gas velocity, static pressure, and temperature. The dependence of gain, temperature, and gas velocity on the primary nitrogen molar flow rate and basic hydrogen peroxide temperature was obtained. A maximum small-signal gain of 7 /spl times/ 10/sup -3/ cm/sup -1/, average gas velocity of 575 m/s, static temperature of 172 K were measured for flow rates of 270 mmole/s of primary nitrogen, 39.2 mmole/s of chlorine, 11 mmole/s of secondary nitrogen, and 0.8 mmole/s of iodine. Estimation of the static pressure in the flow core from spectroscopic data is very close to the static sidewall pressure. The role of transverse velocity components in the gas flow and their effect on the interpretation of gain profiles is discussed.

Efficient chemical oxygen-iodine laser powered by a centrifugal bubble singlet oxygen generator

Efficient production of singlet delta oxygen in a bubble singlet oxygen generator (BSOG) under the influence of centrifugal acceleration, 136g, has been obtained. An output power of 770W with chemical efficiency of 25.6% has been achieved in a small-scale, supersonic chemical oxygen-iodine laser supplied by the centrifugal BSOG. The ratio of the output power to the basic hydrogen peroxide volumetric flow rate was 4.3KJ∕liter. Efficient chemical oxygen-iodine laser (COIL) operation with the centrifugal BSOG demonstrates the potential for mobile COIL applications.

Sub- and supersonic COILs driven by a jet-type singlet oxygen generator

The experimental results of study of sub- and supersonic chemical oxygen-iodine lasers (COIL) based on the jet type singlet oxygen generator are presented. The progress in the high pressure jet type singlet oxygen generators allowed to develop the compact highly efficient COIL. The different types of the mixing schemes were tested in supersonic COIL based on the high pressure jet singlet oxygen generator. The preliminary cooling of the active medium by mixing of oxygen with the cold buffer nitrogen gas results in high efficiency operation of the small scale COIL with subsonic and supersonic gas flow in the laser cavity. In COIL with the fast axial gas flow the chemical efficiency more than 20% was achieved.

HACA's Heritage: A Free-Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars

The hydrogen-abstraction/acetylene-addition (HACA) mechanism has been central for the last decades in attempting to rationalize the formation of polycyclic aromatic hydrocarbons (PAHs) as detected in carbonaceous meteorites such as in Murchison. Nevertheless, the basic reaction mechanisms leading to the formation of even the simplest tricyclic PAHs like anthracene and phenanthrene are still elusive. Here, by exploring the previously unknown chemistry of the ortho-biphenylyl radical with acetylene, we deliver compelling evidence on the efficient synthesis of phenanthrene in carbon-rich circumstellar environments. However, the lack of formation of the anthracene isomer implies that HACA alone cannot be responsible for the formation of PAHs in extreme environments. Considering the overall picture, alternative pathways such as vinylacetylene-mediated reactions are required to play a crucial role in the synthesis of complex PAHs in circumstellar envelopes of dying carbon-rich stars.

Dissociation of Molecular Iodine in a Flow Tube in the Presence of O2(1Σ) Molecules

Molecular iodine dissociates in the presence of O(2)((1)Δ) and O(2)((1)Σ) molecules, but the mechanism of this process is not completely understood. In this paper, using flow tube experiments, we studied the initiation stage of iodine dissociation. Absolute spectral irradiance measurements were employed for measurements of concentrations of electronically excited particles. It was found that under the present experimental conditions initiation of iodine dissociation is mainly caused by reaction O(2)((1)Σ) + I(2) → O(2)((3)Σ) + 2I with a rate constant of (9.3 ± 2.0) × 10(-11) cm(3) s(-1). An appreciable role of the O(2)((1)Δ) molecule as the dissociation initiator has not been observed. It was observed that the growth rate of iodine atoms sharply accelerated when the concentration of I((2)P(1/2)) atoms approached 2 × 10(-4) of O(2)((1)Δ) concentration or when production rates of O(2)((1)Σ) molecules in reactions O(2)((1)Δ) + I((2)P(1/2)) and O(2)((1)Δ) + O(2)((1)Δ) became equal.

Luminescence of the (O2(a1Δg))2 collisional complex in the temperature range of 90-315 K: Experiment and theory

Experimental and theoretical studies of collision induced emission of singlet oxygen molecules O2(a(1)Δg) in the visible range have been performed. The rate constants, half-widths, and position of peaks for the emission bands of the (O2(a(1)Δg))2 collisional complex centered around 634 nm (2) and 703 nm (3) have been measured in the temperature range of 90-315 K using a flow-tube apparatus that utilized a gas-liquid chemical singlet oxygen generator. The absolute values of the spontaneous emission rate constants k2 and k3 are found to be similar, with the k3/k2 ratio monotonically decreasing from 1.1 at 300 K to 0.96 at 90 K. k2 slowly decreases with decreasing temperature but a sharp increase in its values is measured below 100 K. The experimental results were rationalized in terms of ab initio calculations of the ground and excited potential energy and transition dipole moment surfaces of singlet electronic states of the (O2)2 dimole, which were utilized to compute rate constants k2 and k3 within a statistical model. The best theoretical results reproduced experimental rate constants with the accuracy of under 40% and correctly described the observed temperature dependence. The main contribution to emission process (2), which does not involve vibrational excitation of O2 molecules at the ground electronic level, comes from the spin- and symmetry-allowed 1(1)Ag←(1)B3u transition in the rectangular H configuration of the dimole. Alternatively, emission process (3), in which one of the monomers becomes vibrationally excited in the ground electronic state, is found to be predominantly due to the vibronically allowed 1(1)Ag←2(1)Ag transition induced by the asymmetric O-O stretch vibration in the collisional complex. The strong vibronic coupling between nearly degenerate excited singlet states of the dimole makes the intensities of vibronically and symmetry-allowed transitions comparable and hence the rate constants k2 and k3 close to one another.

High gain, high pressure, highly efficient COIL

The activity of development a COIL with high potential recovered pressure, high gain and efficiency is described. Two nozzle banks with conical supersonic nozzles for the driver nitrogen but with different nozzle arrangements have been developed for generation of the gain flow of chemical oxygen-iodine laser. The nozzle banks were supplied by oxygen flow from the cross-flow singlet oxygen generator with filament-guided jets. Results of aerodynamic tests, visualization of flows by laser induced fluorescence, scanning of the excited iodine atoms distribution and laser power extraction are presented. The efficient penetration of the driver buffer flow into the gain flow was observed at distances less than 100 mm from the nozzle banks. The total power exceeding 1 kW with chemical efficiency more than 24% was obtained in 5 cm gain length COIL without helium dilution. The lasing was observed for both nozzle banks at total mirror transmission more than 10%.

Lasing performance of a chemical oxygen iodine laser (COIL) with advanced ejector nozzle banks

Experimental lasing results for the Chemical Oxygen Iodine Laser, (COIL), using four different ejector nozzle configurations are presented. These nozzle banks differed in the location of Iodine injection, the area of the oxygen nozzles, and the nozzle contour of the primary driver nitrogen. The aerodynamic choking of the oxygen jets caused by the under expanded primary driver nitrogen resulted in a reduction of the O2 (1(Delta) ) yield and chemical efficiency. Dilution of chlorine with helium in the ratio of 1:1 reduces the partial pressure of oxygen and increases the velocity resulting in a chemical efficiency of 25% at 250 mmoles/sec and 23% at 500mmoles/sec of driver nitrogen respectively. The corresponding Pitot pressures are 50 and 90 torr.

Optimization of jet singlet oxygen generator for chemical oxygen-iodine laser

Experimental investigation of a jet singlet oxygen generator for a supersonic chemical oxygen-iodine laser was performed aimed to evaluation of the effects of BHP temperature and composition on the water content and other output generator parameters. Laser experiments on a small-scale system were realized to prove the obtained results.

Predicted and measured output parameters of high pressure jet SOG

Jet singlet oxygen generator (JSOG) is one of the most efficient sources of electronically excited O2(1(Delta) ). The JSOG can operate at very high partial O2(1(Delta) ) pressure. This feature of JSOG allows supersonic COIL operation without water vapor trap. The prediction of output parameters of JSOG is very important for correct design and engineering of COIL. The one-dimensional model of JSOG has been developed to predict output parameters (chlorine utilization, O2(1(Delta) ) yield). The comparisons of calculated and measured output parameters are presented. The main attention is paid to discrepancies of calculated and measured output parameters and limitation of the one-dimensional model. It is shown that for extremely high pressure JSOG the role of effects that cannot be included into a one-dimensional model is very important. The difference between input and output BHP temperature in JSOG is correlated with chlorine utilization and O2(1(Delta) ) yield.