V. N. Azyazov

Multi-pathway I2 dissociation model for COIL

Vibrationally excited iodine I2(X,v>20) is an important intermediate in the standard COIL dissociation model. This intermediate is populated by the I* + I2(X) reaction. In this model excitation probabilities for the v-th I2(X) vibrational level γ(v) are critical parameters. In the present study we examined excitation probabilities γ(v) based on the comparison of calculated populations of vibrational levels of iodine molecules with their experimental values. The total excitation probability for I2(X, v>25) was found to be γ(v>25)≈ 0.1. The standard dissociation model with γ(v>25) ≈0.1 cannot provide the observed dissociation rates. Moreover the number of O2(a) molecules consumed per dissociated I2 molecule would exceed 20 if the standard dissociation model is the predominant dissociation pathway, which is at variance with experiment. Barnault et al.3 found that the populations of I2(10≤v≤23) were much higher than ν≥30. Such high populations of I2(10≤v≤23) could be explained by means of direct excitation in the I* + I2(X) reaction. A satisfactory agreement between calculated I2(v) populations and the experimental data was achieved for the total excitation probability γ(v>25) =0.05-0.1 and for γ(15 SPIE LASE PWL 102 2008-01-19|2008-01-24 Lasers and Applications in Science and Engineering PW08L 774378 San Jose, California, United States High Energy/Average Power Lasers and Intense Beam Applications II 6874 COIL and EOIL 1

A simplified kinetic model for the COIL active medium

Kinetic data obtained in the last decade has resulted in revisions of some mechanisms of excitation and deactivation of excited states in the chemical oxygen-iodine laser (COIL) medium. This review considers new kinetic data and presents analyses of the mechanisms of pumping and quenching of electronically and vibrationally excited states in the oxygen-iodine laser media. An effective three-level model of I2 molecule excitation and relaxation has been developed. The calculated effective rate constants for deactivation of I2(X,11&leνle;24) by O2, N2, He and CO2 are presented. A simplified kinetic package for the COIL active medium is recommended. This model consists of a 30-reaction set with 14 species. The results of calculations utilizing simplified model are in good agreement with the experimental data.

On the O 2 ( a 1 Δ) quenching by vibrationally excited ozone

The development of a discharge oxygen iodine laser (DOIL) requires efficient production of singlet delta oxygen (O2(a)) in electric discharge. It is important to understand the mechanisms by which O2(a) is quenched in these devices. To gain understanding of this mechanisms quenching of O2(a) in O(3P)/O2/O3/CO2/He/Ar mixtures has been investigated. Oxygen atoms and singlet oxygen molecules were produced by the 248 nm laser photolysis of ozone. The kinetics of O2(a) quenching were followed by observing the 1268 nm fluorescence of the O2 a → X transition. Fast quenching of O2(a) in the presence of oxygen atoms and molecules was observed. The mechanism of the process has been examined using kinetic models, which indicate that quenching by vibrationally excited ozone is the dominant reaction.

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.

Efficient subsonic chemical oxygen-iodine laser operating without buffer gas

Efficient subsonic chemical oxygen iodine laser operating with small buffer gas flow rate at Mach number M<EQ1 is reported. The highest value of output power of 415 W with chemical efficiency 23% was obtained at Cl2 flow rate of 20 mmole/s. It was found that the power does not almost depend on N2 or CO2 buffer gas flows up to two times higher than oxygen flow rate.

Model of I 2 dissociation in COIL medium taking into account interaction of vibrationally excited iodine and singlet oxygen molecules

The kinetic model of I2 molecules dissociation in chemical oxygen iodine laser (COIL) medium taking into account interaction of the vibrationally excited iodine and singlet oxygen molecules is developed. The results of computer calculations utilizing this model are good agreement to experimental dissociation rate of iodine molecules in the media characteristic of COIL.

Effective operation of subsonic COIL with N 2 and CO 2 buffer gases

The efficient power operation in a chemical oxygen-iodine laser for subsonic modes has been demonstrated. It is shown that the substitution of the buffer gas N2 by CO2 does not cause any significant variation in the dependence of the output power on the degree ofdilution ofthe active medium. The maximum power was 581 W for the flow rate of molecular chlorine 22 mmole/s that corresponds to a chemical efficiency of &eegr;chem = 29%.

Calculation of O2 molecules distribution over vibrational levels in chemical oxygen-iodine laser

The kinetics model of chemical oxygen-iodine laser (COIL) active medium taking into account EE, EV, VV, VT energy transfer processes was proposed. The O2 molecule distribution on the vibrational levels in COIL was calculated. It is suggested that the involving of vibrationally excited O2(a) into pooling reaction can increase the rate of stored in singlet oxygen electronic energy in COIL medium. Approximately 50% of relaxed O2(a) energy transfers into thermal energy.

Molecular singlet delta oxygen quenching kinetics in the EOIL system

The development of a discharge oxygen iodine laser (DOIL) requires efficient production of singlet delta oxygen O2(α1 Δ) in electric discharge. It is important to understand the mechanisms of of O2α1 Δ) quenching in these devices. To gain understanding of this mechanisms quenching of O2(α]1 Δ)in O/O2/O3/CO2/He mixtures has been investigated. Oxygen atoms and singlet oxygen molecules were produced by the 248 nm laser photolysis of ozone. The kinetics of O2(α1 Δ) quenching were followed by observing the 1268 nm fluorescence of O2α1 Δ → X3 Σ transition. It is shown that vibrationally excited ozone O3(υ;) formed in the three-body recombination O + O2 + M →O3(υ) + M is an important O/O2/O3 quenching agent in O/O2/O3 systems. The process O3(υ ≥2) + O2(a1 Δ)→ 2O2 + O is the main O2(α1 Δ) deactivation channel in the post-discharge zone. If no measures are taken to decrease oxygen atom concentration, the contribution of this process into overall O2(α1Δ) removal is significant even in the discharge zone. It was found in experiment that addition of species that are good quenchers of O3(υ;) decrease O2(a1 Δ) deactivation rate in the O/O2/O3 mixtures.

O 2 ( a 1 Δ ) vibrational kinetics in oxygen-iodine laser

Kinetics of vibrationally-excited singlet oxygen O2(a1Δ,ν) in gas mixture O3/N2/CO2 was studied using a pulse laser technique. Molecules O2(a1Δ,ν) were produced by laser photolysis of ozone at 266 nm. The O3 molecules number density was followed using time-resolved absorption spectroscopy. It was found that an upper bound for the rate constant of chemical reaction O2(a1Δ,ν)+ O3 is about 10-15 cm3/s. The rate constants of O2(a1Δ,ν= 1, 2 and 3) quenching by CO2 are presented.