Absorption of CO 2 laser emission by freon-12

The infrared (IR) absorption of freon-12 (CF₂Cl₂) was studied in the emission range of a 3-W tunable CW CO₂ laser by using a brass cell with KBr windows that was located outside the laser resonator. The results show that CF₂Cl₂ absorbs all CO₂ laser emission lines in the ranges of 1073–1083 cm^-1 and 937–943 cm^-1. The most strongly absorbed laser line was 10P (28) ( 937.21 cm^-1). Absorption coefficient values were obtained for all available wavelengths of the CO₂ laser as the CF₂Cl₂ pressure was varied from 5 to 1000 mbar. By using the HITRAN database for freon-12, the absorption coefficients were calculated at the 10P (28) and 9R (28) lines as functions of the gas pressure and compared with the experimental values. The calculated results are in reasonable agreement with the experiment. PACS 33.20.Ea; 42.55.-f; 42.55.Lt     

Laser isotope separation of 13C: A comparative study

IR laser chemistry of (CF₃Br/Cl₂) mixture and neat CF₂HCl are examined in the context of ¹³C enrichment. Decomposition extent, enrichment factor and energy absorbed are measured for both systems at their respective optimum conditions. A direct comparison is obtained by keeping extraneous factors such as laser, its pulse duration, cell, irradiation geometry etc. the same. The halogen scavenged CF₃Br MPD requires lower fluence compared to neat CF₂HCl irradiation. Overall throughput for a product with 60–65% ¹³C content in a single stage is the same for both systems requiring a similar amount of energy. However, at lower enrichment levels, CF₂HCl MPD is better than (CF₃Br/Cl₂) photolysis in terms of both product yield and energy absorption.     

Carbon-13 enrichment by IR laser chemistry of CHF3-Cl2

IR laser chemistry of CHF₃ is investigated in both neat form and in the presence of Cl₂ for carbon-13 enrichment. Infrared multiple-photon dissociation of CHF₃ is an order of magnitude more efficient in the scavenged system compared to the neat case. The photolysis of CHF₃/Cl₂ mixture results in two products, viz., CF₂Cl₂ and C₂F₄Cl₂ but with different enrichment factors. The parametric studies show that C₂F₄Cl₂ arises due to MPD of CF₂Cl₂ in secondary photolysis.     

cw far-infrared lasing in15NH3, stark resonantly pumped by a CO2 or N2O laser

CF₂ClCF₂Cl and ethyl acetate have absorption bands of similar width centered at the same frequency. Kinetics of the decompositions of these compounds by a cw CO₂ laser have been studied over a range of laser frequencies extending to 25 cm^?1 below band center. At constant translational temperature and pressure, the CF₂ClCF₂Cl rate constant changes by more than 200 with frequency, while the corresponding change for ethyl acetate is at most 3. The effect of laser frequency increases with increasing CF₂ClCF₂Cl pressure, while the reverse is true in ethyl acetate. Arrhenius plots show activation energies independent of both frequency and pressure.     

氟里昂113在多频强红外场离解过程中的V-V能量转移

用TEACO₂激光9P(24),9P(22),9P(20),9P(18)四支线组成的多频强红外场“超激发”氟里昂₁₁₃分子,使其达到很高激发态。由分解曲线可以看出CF₂Cl·CFCl₂与CF₃·CCl₃之间的V-V能量转移有明显的“虹吸”作用。从所得主要产物C₂P₆,C₂Cl₆,C_关键词：     

Effect of rotational relaxation on the yield of the multiphoton dissociation of CF3Cl and CF3Br under TEA-CO2 laser pulses

The yield of the multiphoton dissociation of CF₃Cl and CF₃Br induced by TEA-CO₂ laser pulses has been studied in the pressure range between 0.25 and 8 Torr, the laser wavelength being chosen so as to excite preferentially the minor isotopic components¹³CF₃Cl and¹³CF₃Br. For both compounds the dissociation probability is found either to increase almost linearly or to decrease monotonously with gas pressure, according as the laser beam is focused or unfocused, respectively. This behaviour is explained by rotational relaxation effects, and a value of 22ns·Torr for the rotational self-relaxation time of CF₃Cl is obtained.     

TEA CO2 laser-induced photodissociation of UF6 via interspecies V-V energy transfer from multiple photon excited halomethanes

The dissociation of UF₆ sensitized by multiple photon excitation of a series of halomethanes: CF₄, CF₃Cl, and CF₂Cl₂ has been investigated. The roles of various experimental parameters like exciting frequency, fluence and pressures of sensitizer/UF₆ on the dissociation yield were studied to examine (1) the characteristics of the sensitizer/UF₆ system and (2) the coupling of vibrational energy between two molecular systems. The efficiency of the energy transfer process was estimated on the basis of long range dipole-dipole interaction to gain an understanding of the dissociation process.     

Pressure dependence of laser oscillation and superfluorescent emission from an optically pumped CF4 laser

Experiments on pressure dependence of a CF₄ laser have been carried out to elucidate dynamic characteristics of CF₄ molecules pumped by CO₂ lasers. The results are followed by a model calculation which characterizes collisional quenching of the energy levels related to the stimulated emission. The enhancement of the laser output induced by buffer-gas addition, which was found under specific conditions, is discussed in relation to the competition between laser and superfluorescent emissions.     

Infrared spectrum and molecular force field of CF2Cl2

The infrared spectrum of CF₂Cl₂ has been measured under medium resolution in the range 1600-400 cm^?1. More than 100 bands including fundamental, overtone, combination, and “hot” bands of the three isotopic species CF₂³⁵Cl₂, CF₂³⁵Cl³⁷Cl, and CF₂³⁷Cl₂ have been identified. The band contour studies have enabled the fundamental vibrations to be unambiguously assigned, including the modes ν₃ and ν₇, the positions of which were previously in doubt. The observed values for CF₂³⁵Cl₂ in conjunction with the frequency shift data for CF₂³⁵Cl³⁷Cl and CF₂³⁷Cl₂ have been used in determining a general valence force field, which adequately describes the system investigated. A Fermi resonance interaction between ν₈ and ν₃ + ν₉ levels for the three isotopic species has been interpreted. The corresponding perturbations between those levels obtained by adding ν₂ or ν₅ to both ν₈ and ν₃ + ν₉ have also been found and the related features carefully investigated.     

Effect of gas pressure and pulse length on the isotopically selective multiphoton dissociation of CF3Cl under CO2 laser pulses

The multiphoton dissociation of CF₃Cl induced by TEA-CO₂ laser pulses has been studied in a focused beam geometry. TheR(10) [00°1–02°0] ( ) laser line was used, so as to dissociate preferentially the minor isotopic component¹³CF₃Cl. The isotopic selectivityS and the dissociation probability per pulse ω were measured in the pressure range between 0.25 and 8 Torr. With short laser pulses (90 ns FWHM),S is found to increase slightly with gas pressure up to 2 Torr, and ω, to increase almost linearly over the whole pressure range studied. A schematic model is proposed which satisfactorily explains these results if the transition rates across the energy level spectrum of the CF₃Cl molecules are assumed to increase with gas pressure.     

Submillimeter laser action of CW optically pumped CF2Cl2 (Fluorocarbon 12)

Eleven new CW far infrared (FIR) laser lines have been observed in the 600 m–1200 m range from the CF₂Cl₂ (Fluorocarbon 12) molecule optically pumped by a CO₂ laser. A 510^–4–10^–3 accuracy is achieved in the measurement of the FIR wavelengths.The frequency offset between the CO₂ pump center and the absorption line centers are measured using the transferred Lamb dip technique. Owing to a recent spectroscopic study of the CF₂ ³⁵Cl₂ molecule three lines may be assigned with great confidence as rotational transitions in thev ₆ vibrational band 923 cm^–1 of this main isotope.     

Parametric study of the IRMPD of CF2HCl molecules with the 9P22 CO2 laser line

The separation of ¹³C by infrared multiple photon decomposition (IRMPD) of CF₂HCl has been parametrically studied in relation with some key parameters such as the laser fluence, the number of laser pulses, and the gas pressure. The process selectivity, the depletion of the ¹³C isotope in the residual gas, the relative amount of ¹³C separated per pulse, and the energy expenditure were determined as a function of the above mentioned parameters, and conclusions were drawn concerning the efficiency of the separation process. An isotopic selectivity of about 40 was obtained in the investigated range of pressure. At 10 Torr of pure CF₂HCl, the ¹³C depletion in the residual gas was 45% when only 300 laser pulses were used. A maximum amount of 4.6×10^–10 kg ¹³C separated per pulse was obtained.     

Spectroscopic investigation of the plasma of a high-current diffuse discharge in He/Ar/CF2Cl2(CCl4) mixtures

Survey emission spectra in the region of 190–600 nm and time and service-life characteristics of a transverse nanosecond discharge in He/Ar/CF₂Cl₂(CCl₄) mixtures at a pressure of 10–100 kPa are investigated. In the emission spectra, excited products of the decomposition of freons—C₂(A−X), CN(B−X), Cl ₂ ^* , C^*, Cl^*, and Cl^+*— and the emission of ArF at λ=193 nm are revealed. The emissions of Cl ₂ ^* at λ=258 nm and ArF at λ=193 nm were the most intense. The discharge in the He/Ar/CF₂Cl₂ mixture is a multiwave emission source with λ=258 nm Cl ₂ ^* 193 nm ArF, and probably, 175 nm Arcl. It is of interest for applications in UV-VUV-range pulse photometry. The duration of the emission on Cl ₂ ^* , ArF, ArI, ClI, and ClII transitions in the discharge in the Ar/CF₂Cl₂ mixture (P=10–20 kPa) was 200–300 nsec. With adding He and increasing pressure to 100 kPa the duration of the emission decreased by a factor of 1.5–2. The basic mechanisms of the formation of Cl₂, ArF, and CN(B) molecules in the transverse-discharge plasma are considered. Uzhgorod State University, 46, Pidgirna Str., Uzhgorod, 294000, Ukraine. Translated from Zhurnal. Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 241–246, March–April, 1999.     

Diode-laser radiation absorption of CF2Cl2 around 921 cm−1 in a supersonic jet

With a diode laser we have studied the spectral region around 921 cm^–1 of the CF₂Cl₂ molecule cooled in a free jet. Accurate studies of the intensity of two vibrorotational bands have enabled us to determine their assignment. In addition, the rotational structure has been partially resolved, and approximate fitting parameters have been deduced. The simultaneous use of a diode laser and a free jet has proved to be useful in correctly identifying the origin of the absorption bands.     

Zur plasmachemischen Umsetzung von GaAs mit CCl4 und CF2Cl2 in Gegenwart von Sauerstoff

The halogen liberation and reaction with GaAs by a plasma discharge in a flow reactor, using CCl₄, CF₂Cl₂ and CCl₄/O₂, CF₂Cl₂/O₂ mixtures was measured. The yields were studied in dependence from the output of a 27 MHz radio-frequency generator and from the oxygen content of the etching gas. A simple model of the kinetics is introduced to discuss the experimental results.     

Optoacoustic cross-section measurements for ir pulses: CO2 laser absorption by CF3I

The pulsed optoacoustic method is studied to measure absolute infrared multiphoton absorption cross sections. The influence of the thermalisation by the walls of the cell is shown to be very important at low pressure. This influence is analysed both experimentally and theoretically by solving the coupled diffusion and relaxation equations for vibrational and translational energies. The sensitivity of the method is limited by a spurious pressure signal present even with non-absorbing gases. This parasitic signal is attributed to an absorption located on the inner surface of the windows of the cell. For instance, using KCl windows, the observed spurious signal corresponds to about 10⁻⁴ of the total laser energy, transmitted from the windows to the gas. This proportion is independent on the energy fluence. Taking care of these limitations, we have measured the absorption cross section of CF₃I at the different wavelengths of the (001–020) transitions of the CO₂ laser. The typical energy fluences in these experiments were varied from 10⁻³ to 1J/cm². To be in collision free conditions, the CF₃I pressure was made equal to 0.2 Torr.     

High-resolution spectroscopy of CF2Cl2 in a molecular jet

Absorption spectra of CF₂Cl₂ were recorded around 923 cm^–1, with a resolution of 50 MHz. The application of the molecular jet technique considerably simplifies the spectra as compared to room-temperature experiments. Rotational and vibrational temperatures were measured for CF₂Cl₂ pure and seeded in Ar or He. Molecular constants were obtained for thev ₆ vibrational band of the two most abundant chlorine isotopic species, as well as vibrational band origines for thev ₆±v ₄ and thev ₆±v ₅ hot-bands of the CF₂ ³⁵Cl₂ isotope.Guest     

The frequency,fluence and pressure dependence of the absorption of pulsed CO2-laser radiation by CF2HCl

Absorption measurements in the CF₂HCl fundamental vibrational band v₃, and combination band v₅ + v₉, for laser energy fluence between 0.1–1.2 cm⁻² and 1–100 Torr gas pressure, are reported. Three distinct regions are experimentally observed for the fluence dependence of the absorption cross section σ and the average number of absorbed photons <n>. Adding Ar buffer gas to CF₂HCl enhances the absorption efficiency only in the v₃ band.     

Catalytic action of the products of photodissociation of some atmospheric impurities on water vapor condensation

A significant effect of the photodissociation products of atmospheric impurities, such CF₂Cl₂, CCl₄,H₂S, and NH₃, on the condensation of supersaturated water vapor is demonstrated. The experiments are performed in a cloud chamber, with irradiation being carried out by an ArF excimer laser (λ = 193 nm). The results obtained in the absence and presence of photodissociation are interpreted. The impact of the initial water vapor pressure in the chamber on the process of condensation is observed and explained.     

Dynamics of molecules excited by infrared laser radiation

The CF₂HCl and CF₂Cl₂ molecules upon multiphoton excitation are investigated by the method of Raman light scattering spectroscopy at frequencies of fundamental transitions. It is demonstrated that essentially nonequilibrium energy distribution of molecules is formed in the process of excitation. Physical parameters characterizing this distribution are determined.