F. W. Lee

Photolytic spectroscopy of simple molecules. II. The production of 6P atoms from the X 1Σg state of Cs2

In this work the two‐photon technique for the study of selective photolysis described in the preceding article was used for the measurement of the relative cross sections for the photolysis of Cs2 into each of the energetically possible product channels that could have been reached at wavelengths in the range from 445 to 640 nm. The resulting dispersion curves showed three relatively broad absorption bands, each leading to a different distribution of population among the product states. A relatively broad band in the blue region of the spectrum was found to yield an inverted branching ratio for dissociation which favored the more highly excited product by a factor of better than 50 to 1. This particular result implied that continuous wave, stimulated emission should be obtained from the 5 2D3/2→6 2P1/2 transition of atomic cesium with adequate photolytic pumping of Cs2 at blue wavelengths. An analysis of the complete photolysis spectrum obtained in this work indicated that both dissociation and predissoci...

Measurement of the rate coefficients for the bimolecular and termolecular de‐excitation reactions of He(2 3S) with selected atomic and molecular species

This work reports the measurement of second and third order excitation transfer reactions of metastable 2 3S helium atoms with 15 reactants selected because of their widely varying values of polarizability and dipole moment. In this study He(2 3S) destruction frequencies have been experimentally determined from measurements of the optical absorption of the 3889 A, 2 3S →33P, helium transition in high pressure afterglows of mixed gases excited by intense electron beam discharges. Data have been obtained as functions of helium pressure over the range 800–2000 Torr and as functions of the partial pressure of reactant from 14 to 200 mTorr. From this data pressure dependent rate coefficients have been extracted and subsequently resolved into contributions from second order, bimolecular, and third order, termolecular components. The bimolecular components have been found to agree with tabulated values appearing in the literature. The sensitivity of the method has been sufficient to detect termolecular component...

Measurement of the rate coefficients for the bimolecular and termolecular ion–molecule reactions of He2+ with selected atomic and molecular species

This work reports the measurement of bimolecular and termolecular charge transfer reactions of He2+ into nonassociative product channels. In this study ion destruction frequencies have been experimentally determined from the selectively excited fluorescence of N2+ in high pressure afterglows of mixed gases excited by intense electron beam discharges. Data have been obtained as functions of helium pressure over the range from 400 to 1500 torr and as functions of the partial pressure of reactant from 50 to 200 mtorr. From these data pressure‐dependent rate coefficients have been extracted and subsequently resolved into contributions from bimolecular and termolecular components for reactions of He2+ with Kr, H2, O2, NO, HBr, HCl, H2O, N2O, NO2, C3H8, NH3, and CCl2F2, selected because of their widely varying values of polarizability and dipole moment. The bimolecular components have been found to agree with the NOAA flowing afterglow results, where available, and to compare favorably with theoretical values o...

The coherent and incoherent pumping of a gamma ray laser with intense optical radiation

Both the coherent and incoherent pumping with intense optical radiation of electromagnetic transitions in nuclei were modeled in this work. In the first case the anti‐Stokes upconversion of conventional laser radiation was shown to be a potentially viable means for pumping a γ‐ray laser. With the most favorable possible arrangement of nuclear energy levels, the threshold for stimulated output at 10 keV might be reached at a few tens of Joules for isomeric media with lifetimes of the order of tens of years. Whether such an arrangement of excited states actually exists will require additional experimentation. In the case of the incoherent pumping of nuclear material, the resonant excitation of energetic states of nuclei by x radiation from laser plasmas or exploding wires was modeled with results similar to those for the case of coherent pumping. Thresholds for stimulated output could be as low as a few hundred Joules into the primary laser pulse producing the x‐ray flash. Again the possibilities were found...

Gain and saturation of the atomic fluorine laser

In this work a dilute fluorine plasma pumped by the ion‐ion recombination of H+2 and F− has been operated as a pulsed amplifier. Two synchronously excited plasmas were produced by preionized discharges in an atmospheric electrical avalanche device switched by hydrogen thyratrons. Two principal outputs having wavelengths of 745 and 635 nm were obtained from the tube serving as an oscillator. These were dispersed so that they could be individually threaded through the second discharge. Calibrated attenuation of the beam from the oscillator subsequently injected into the amplifier provided data on the overall amplification ratio. From these data effective saturation intensities of 1.2 and 4.5 kW/cm2 were found for the transitions at 745 and 635 nm, originating on the 3p4P05/2 and 3p4S03/2 states of F*, respectively. Corresponding small signal gains were found to be extremely high, reaching 0.44 and 0.31 cm−1, for the two transitions, respectively.

Measurement of the rate coefficients for the de‐excitation reactions of He2 (3Σu) metastables with Ne, Ar, N2, CO, CO2, and CH4

This work reports the measurement of the excitation transfer reactions of metastable He2(3Σu) helium molecules with Ne, Ar, N2, CO, CO2, and CH4. In this study He2(3Σu) destruction frequencies have been experimentally determined from measurements of the optical absorption of the 4650 A, 3Σu →3πg helium transition in high pressure afterglows of mixed gases excited by intense electron beam discharges. Data have been obtained as functions of helium pressure over the range from 1500 to 2500 torr and as functions of the partial pressure of reactant from 14 to 200 mtorr. From this data pressure independent rate coefficients have been extracted which describe the effective bimolecular rates of reaction. These bimolecular rate coefficients have been found to range from 4.4×10−11 cm3 sec−1 for reactions with Ne to 95 ×10−11 cm3 sec−1 for reactions with CO2. Reaction probabilities have been found to be generally larger than for the corresponding reactions of He(23S) metastable atoms, approaching unity for the react...

Pressure dependence of the reaction of He2(3Σ) metastable molecules with Ar

This paper reports the re‐examination and analysis of data characterizing the excitation transfer reaction of metastable He2(3Σu) helium molecules with argon atoms. Data were originally obtained from measurements of the transient optical absorption of the 4650 A, 3Σu→3πg helium transition in high pressure, e‐beam afterglows, and in low pressure, electric discharges. Rate coefficients have been obtained from the data and resolved into components describing the bimolecular and termolecular reactions of He2(3Σu) with Ar. Values of 1.5×10−10 cm3 sec−1 and 2.4±0.8×10−30 cm6 sec−1, respectively, were found. The former corresponds to a reaction probability of 0.18 and the latter represents the first measurements of a termolecular excitation transfer reaction of He2(3Σu).

Modeling of ion–molecule reactions at high pressures

Reported here is a model of ion–molecule reactions that includes a variety of constituent steps which might be appropriate in an environment at atmospheric pressures. A fairly general structure has been assumed for the type of reaction complex that might be assembled from the reacting partners and both coherent and incoherent processes of excitation of the complex have been included in the model. The transition to the product state was modeled as a simple predissociation. From these considerations a comprehensive reaction rate matrix was constructed that described the transition rates between each pair of levels of the complex for a particular set of experimental parameters. The smallest eigenvalue of such a rate matrix was found to generally correspond to an eigenvector of populations that reasonably described the decay of the original reacting species. Since the reaction of He+2 with N2 at atmospheric pressures was the best characterized of the systems appearing in the literature, it was chosen as a veh...

Reactivity of metastable helium molecules in atmospheric pressure afterglows

This work focuses upon previously encountered problems that have impeded the understanding of the role of He2(3Σu) metastable molecules in the afterglows of electrical discharges into atmospheric pressures of helium containing admixtures of reactants. New data are reported that generally confirm the literature values for the reactivities of this species at high pressures and continue the disagreement with earlier measurements in low pressure plasmas. Results are presented for reactions with HCl and HBr for the first time. A study of systematic dependencies of rates upon molecular parameters is reported which shows that the ratio for bimolecular reactions of vibrationally excited and unexcited He2(3Σu) molecules is largely independent of the identity of the reacting partner. This provides a means for using data on the pressure dependent part of the effective rate of reaction of He(2 3S) atoms to estimate the rate coefficients for the bimolecular reactions of the more elusive He2(3Σu) molecule.

Gain, saturation, and optimization of the XeF discharge laser

In this work a xenon‐F2 plasma diluted in helium has been operated as a pulsed amplifier for the B→X transition of XeF. Two synchronously excited plasmas were produced by preionized discharges in atmospheric electrical avalanche devices switched by hydrogen thyratrons. The principle output obtained at 352 nm from the tube serving as an oscillator was optically delayed and then was threaded through the second discharge. Calibrated attenuation of this beam injected into the amplifier provided data on the overall amplification ratio. From these data effective saturation intensities of 620 and 860 kW/cm2 were found for operation at pressures of 2.7 and 3.7 atmospheres, respectively. Corresponding small signal gains were found to be moderately high, reaching 0.11 and 0.13 cm−1, for the two conditions, respectively. Based upon these results for the gain and saturation parameters, a self‐excited oscillator was designed to be optimized simultaneously for energy density and efficiency. By matching the ringing time...