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An efficient, all-sky input optical system has been mated to a 100-mm-aperture Fabry–Perot interferometer that employs a cooled (−150 °C) CCD as a photon detector to create an all-sky Doppler interferometer. The instrument is capable of simultaneously measuring Doppler shifts and widths of nightglow emission lines from many different points in the sky, thereby providing determinations of upper-atmosphere neutral wind and temperature fields over a large region (to ≈2000 km in extent). For OI 630-nm (thermosphere) and OH 799.6-nm (mesopause) nightglow emissions, exposure times of 5–15 min provide good-quality interferometric images. The capability of the all-sky Doppler interferometer is illustrated by examples of thermospheric wind and temperature fields measured over Millstone Hill, Massachusetts.

An account is given of laboratory studies made over 50 years ago that revealed a very fast electron-ion recombination process and the subsequent experiments that established the underlying mechanism. These studies were facilitated by development during World War II of major new technologies such as microwaves and fast electronics. Many of these developments took place at MIT in its classified Radiation Laboratory. In 1946, these extensive facilities were converted to the Research Laboratory for Electronics, where Physics Professors W. P. Allis and S. C. Brown formed the Microwave Discharge Group, initially with four graduate student experimenters.

A novel design of a rf afterglow source of the oxygen forbidden lines at 630.0 and 557.7 nm for use in thermospheric dynamics studies is presented. With a repetitive discharge-afterglow excitation cycle, the source yields adequate afterglow intensities of the OI lines that are sufficiently free of background continuum for use in Fabry-Perot interferometer measurements of spectral line profiles. These lines provide accurate zero-velocity references in Fabry-Perot determinations of Doppler shifts in the OI thermospheric lines. The design considerations for the rf source are described, together with its preparation and filling by an ultrahigh-vacuum gas-handling system. Examples are given of the source's output spectrum, as measured by a grating spectrometer, and its spectral line profiles, as determined by a Fabry-Perot interferometer. Comparative interferometry between the OI afterglow source lines and nearby (within approximately 0.01-0.02-nm) lines from hollow-cathode sources illustrates the means of establishing secondary reference sources in cases in which the primary OI afterglow source is not available.

A novel all-sky Doppler interferometer (ASDI) has been used to measure Doppler shifts and widths of nightglow emission lines from the upper atmosphere, thereby permitting determination of the neutral wind and temperature fields over regions up to 2000 km in diameter. The ASDI instrument consists of efficient all-sky (160 degree(s) field-of-view) input optics, a 100 mm aperture Fabry-Perot interferometer and output optics which focus 5 orders of the interference ring pattern superposed on the sky image onto a 512 X 512 pixel, LN2-cooled (-150 degree(s)C) CCD detector. Good quality CCD images of the midlatitude nightglow oxygen 630.0 nm red line (approximately equals 300 km altitude) and 557.7 nm green line (approximately equals 105 km altitude) and the OH 799.4 nm line (approximately equals 86 km altitude) are obtained in 5 - 15 min exposures. The image signal-to-noise ratio is sufficient for division of the 5 circular interference rings into 24 equal azimuthal sectors, so that Doppler shifts and widths for 120 distinct regions of the sky can be obtained from one exposure. Wind and temperature fields derived from the ASDI nightglow 630 nm measurements are compared for observations following the autumnal and the vernal equinoxes.

Midlatitude F-region neutral winds and temperatures determined from Fabry-Perot interferometer measurements of the doppler shifts and widths of nightglow 630.0 nm line profiles are presented for the priority regular world day 14 August 1980. They exhibit, in many respects, the observed behavior for other summer, geomagnetically quiet nights at solar maximum. The neutral temperature decreases from ∼ 1500°K after sunset (21 h LT) to a minimum of ~ 1200°K before dawn (05 h LT), except to the north of the observatory. The zonal winds are eastward at sunset at ∼ 50 m/sec, decrease to zero at ∼ 02 h LT and are westward just before dawn. The meridional winds are zero just after sunset and reach a maximum equatorward value of ∼ 50–70 m/sec at local midnight but do not decrease as predicted; instead, they remain at roughly these values towards dawn. The NCAR thermospheric general circulation model (TGCM) is used to predict the global upper atmospheric temperature and circulation patterns for this world day. The model predictions agree with the measured neutral temperatures and exhibit qualitative similarities to the measured neutral winds. It is concluded that inclusion in the model of ion drift at midlatitudes should improve the agreement with observations.

A microwave-afterglow mass-spectrometer apparatus has been used to determine the dependence on electron temperature T/sub e/ of the recombination coefficients ..cap alpha.. of the hydronium-series ions H/sub 3/O/sup +/ x (H/sub 2/O)/sub n/. For n = 1--3, we find ..cap alpha.. (37/sup +/) = (2.5 +- 0.5) x 10/sup -6/ (300/T/sub e/ (K))/sup 0.08/, ..cap alpha.. (55/sup +/) = (3.0 +- 0.6) x 10/sup -6/ (300/T/sub e/ (K))/sup 0.08/, and ..cap alpha.. (73/sup +/) = (3.6 +- 0.7) x 10/sup -6/ (300/T/sub e/ (K))/sup 0.00/ cm/sup 3//sec over the range 300--400 K < or = T/sub e/ < or = 6000--8000 K and T/sub gas/ = T/sub +/ = 300--400 K. For n = 4 and 5, ..cap alpha.. (91/sup +/) approx. = ..cap alpha.. (109/sup +/) approx. 5 x 10/sup -6/ cm/sup 3//sec, with no apparent dependence on T/sub e/. These results for the higher hydrates differ somewhat from those obtained by Leu, Biondi, and Johnsen. The very weak dependence of ..cap alpha.. on T/sub e/ is quite similar to the behavior noted for the NH/sub 4//sup ts+/ x (NH/sub 3/)/sub n/ cluster ions.

The electron-temperature dependence of the recombination of mass-identified N${\mathrm{O}}^{+}$ ions with electrons is studied by means of a microwave-afterglow/mass-spectrometer apparatus employing microwave heating of the electrons. Under conditions where the N${\mathrm{O}}^{+}$-ion wall current satisfactorily tracks the volume electron density decay, the electron decay data indicate that the recombination coefficient, $\ensuremath{\alpha}(\mathrm{N}{\mathrm{O}}^{+})$, decreases as ${T}_{e}^{\ensuremath{-}(0.37\ifmmode\pm\else\textpm\fi{}0.03)}$ over the range $380\ensuremath{\le}{T}_{e}\ensuremath{\le}5470$ K with ${T}_{+}={T}_{n}=380$ K. The values of $\ensuremath{\alpha}(\mathrm{N}{\mathrm{O}}^{+})$ obtained at ${T}_{e}={T}_{+}={T}_{n}=300 \mathrm{and} 380$ K are (${4.3}^{7}$\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ and (${3.5}^{0}$\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec, respectively. These values apply to N${\mathrm{O}}^{+}$ ions in their ground electronic and probably the $v=1 or 0$ vibration state, and are in good agreement with previous afterglow measurements. Our ${T}_{e}^{\ensuremath{-}0.37}$ variation agrees qualitatively with theoretical predictions of a $\ensuremath{\sim}{T}_{e}^{\ensuremath{-}0.5}$ variation, but is not in agreement with the $\ensuremath{\sim}{T}_{e}^{\ensuremath{-}0.83}$ variation obtained for N${\mathrm{O}}^{+}$ ($v=0$) ions using ion-storage techniques. We are unable to account for the discrepancies in the energy dependences obtained in the two measurements.

Recent observations have shown that, prior to the onset of equatorial spread-F, there exists an altitude modulation in bottomside F-region electron density contours. It has generally been accepted that such a modulation is caused by internal-gravity waves propagating upward from below. In this brief note we suggest that gravity waves may be generated in situ, via the wind shear mechanism. Theoretical calculations and some observations indicate that large wind shears can occur during early evening hours in the low latitude thermosphere. We show that the wind shear may possibly generate gravity waves with horizontal wavelengths on the order of a few hundred kilometers, which is the scale of the observed electron density modulation.

Nightglow 6300-A intensity suppression and enhancement transients have been observed in conjunction with heating of the F region ionospheric electrons in Arecibo ionospheric modification experiments (IME). Ohmic heating of the electrons during X mode propagation of the heating wave results in a ∼1.3% suppression of intensity, in semiquantitative agreement with the suppression predicted for ΔTe ≃ 130°K (measured by the backscatter radar). The 6300-A intensity enhancements (∼6 R) associated with O mode propagation of the heating wave are far too large to be produced by ohmic heating (a value ΔTe ∼ 900°K, about 5 times larger than the backscatter measured value, would be required), suggesting electron acceleration by strong plasma waves that are generated by the heating RF wave. The O(¹D) lifetimes determined from the time constants of the 6300-A intensity enhancement transients yield an F region quenching coefficient k(N2) ≃ 6 to 8 × 10−11 cm³/s, in good agreement with the Platteville IME and with laboratory results.

The paper examines the recombination of electrons with ammonium-series cluster ions, NH4(+)-(NH3)n, for two reasons: (1) NH4(+) may be a significant ion in the lower atmospheres of the earth and the outer planets, and (2) to investigate the weak temperature dependence of the cluster ion's recombination coefficient. A microwave afterglow mass spectrometer was used to determine the recombination coefficients for the first five members of the ammonium series, (18+) through (86+), at temperatures between 200 and 410 K. The electron temperature dependence of the recombination coefficient was determined for (35+) and (52+), the n = 1 and 2 cluster ions, over the temperature range 300-3000 K.

Radiative charge-transfer coefficients for single-electron transfer between doubly or singly charged noble-gas ions and noble-gas atoms have been determined at thermal energy using a drift-tube mass-spectrometer apparatus. At 300 K, $k({\mathrm{He}}^{2+}+\mathrm{He})=(4.8\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{3}$/sec, with slightly smaller coefficients for the reactions ${\mathrm{Ne}}^{2+}$ + Ne, ${\mathrm{Ar}}^{2+}$ + Ar, ${\mathrm{Kr}}^{2+}$ + Kr, and ${\mathrm{Xe}}^{2+}$ + Xe. Differences in reactivity are found for the different, low-lying $^{1}S$, $^{1}D$, and $^{3}P$ states of the doubly charged ions. A three-body contribution to the radiative process is noted, with rate coefficients ranging between ${10}^{\ensuremath{-}31}$ and ${10}^{\ensuremath{-}30}$ ${\mathrm{cm}}^{6}$/sec at 300 K for the different noble-gas systems. The radiative charge-transfer coefficients for singly ionized ions are somewhat smaller, $k({\mathrm{He}}^{+}+\mathrm{Ne})\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{3}$/sec and $k({\mathrm{Ne}}^{+}+\mathrm{Ar})\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{3}$/sec at 300 K. The measured value of $k({\mathrm{He}}^{2+}+\mathrm{He})$ is in reasonable agreement with the very recent theoretical calculations of Cohen and Bardsley.

Microwave afterglow and grating spectrometric apparatus are used to study dissociative recombination in krypton. Over the electron temperature range $300\ensuremath{\le}{T}_{e}\ensuremath{\le}8400$ K and with ${T}_{+}={T}_{\mathrm{gas}}=300$ K, the total rate coefficient may be represented by $\ensuremath{\alpha}[{{\mathrm{Kr}}_{2}}^{+}]=1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}{[\frac{300}{{\mathrm{T}}_{e}(\mathrm{K})}]}^{0.55}$ ${\mathrm{cm}}^{3}$/sec, with an uncertainty of \ifmmode\pm\else\textpm\fi{} 10%. At thermal energy (300 K) excited states of Kr* having energies up to that of the ${\mathrm{Kr}}_{2}^{+}$ ion in its ground electronic and vibrational state are observed to result from the dissociative recombination. With microwave heating to ${T}_{e}\ensuremath{\sim}7000$ K, additional, higher-lying Kr* states (up to \ensuremath{\sim} 0.5 eV above the ${\mathrm{Kr}}_{2}^{+}$ ion ground state) are observed. In both cases the excited states most strongly populated by dissociative recombination appear to be the $5p$ states.

A microwave-afterglow mass-spectrometer apparatus employing microwave heating of the electrons has been used to determine the dependence on Te of the recombination coefficient of electrons with HCO(+) ions. By comparison of the observed electron-density decays to the computed behavior of a recombination- and ambipolar-diffusion-controlled afterglow, it is found that the Te dependence of the recombination coefficients follows a power law with an index of -0.69 + or - 0.07 over the range Te = 293-5500 K. The magnitude of the recombination coefficient is similar to that observed and calculated for simple diatomic ions, while the temperature dependence is somewhat stronger than the Te exp -0.5 dependence predicted by a simplified theory for diatomic ions.

Observing resonances in cross‐section‐versus‐energy curves has long been a way of life for nuclear and particle physicists, for whom this is often the only way to detect short‐lived quantum states. Atomic physicists, on the other hand, have traditionally used other means for observing internal energy states of atoms and molecules. But sixteen years ago a resonance in the cross section for electrons scattering off helium changed the tradition, and by now there is a long catalog of observed resonances in atoms and molecules and an accompanying body of theoretical work that seeks to account for the newly discovered states and explain their behavior.

An all-sky-mapping filter photometeer has been used to study equatorial 630.0 nm nightglow intensity depletions. A generally eastward drift of the ∼ 0m/sec. At times two airglow depletions moving at different velocities were observed simultaneously; in one case they merged. Simultaneous interferometric determinations of doppler shifts in the 630.0 nm line indicated that the velocity of the neutral atmosphere does not appear to be correlated with the drift of the airglow depletions. The results are compared with other observations.

The mobilities of the doubly charged rare-gas ions He/sup 2 +/, Ne/sup 2 +/, Ar/sup 2 +/, Kr/sup 2 +/, and Xe/sup 2 +/ in their parent gases have been determined in a drift-tube mass-spectrometer apparatus. The finding of more than one mobility for each of the doubly charged ions (with the exception of He/sup 2 +/) is attributed to the presence of the /sup 3/P, /sup 1/D, and /sup 1/S long-lived, lowest-energy states of these ions. At 300 K the reduced mobilities (in units of cm/sup 2//V sec) extrapolated to zero field have the values ..mu../sub 0/(He/sup 2 +/ in He) = 18.3; ..mu../sub 0/(Ne/sup 2 +/ in Ne) = 6.5(/sup 1/D), 7.0(/sup 3/P), 8.5(/sup 1/S); ..mu../sub 0/(Ar/sup 2 +/ in Ar) = 2.7(/sup 3/P), approx. 2.2(/sup 1/D); ..mu../sub 0/(Kr/sup 2 +/ in Kr) = 1.11 and 1.28; ..mu../sub 0/(Xe/sup 2 +/ in Xe) = 0.65 and 0.75. The measured values are accurate to +- 3%.

Fabry-Perot inteferometer determinations of thermospheric temperatures from 630.0-nm nightglow line-width measurements have been carried out for the period April-August 1983 from Arequipa, Peru (16.4-deg S, 71.5-deg W geographic; 4.4-deg S magnetic). The nightly variation of the thermospheric temperature T(n) measured on 62 nights is compared with MSIS model predictions and found to agree occasionally with the model but, on average, to exceed model predictions by about 180 K. The largest differences, 400-500 K, often occur during strongly increasing geomagnetic activity such as sudden commencements. The rapid increases in T(n) may result from energetic neutrals precipitating at low latitudes from the ring current or from energy carried to equatorial regions from high-latitude (auroral oval) heat sources by gravity waves and equatorward neutral winds.

A 150 mm aperture, pressure scanned Fabry-Perot interferometer has been used to study the midlatitude twilight and nightglow sodium D-line profiles. The line width measurements during evening and morning twilight indicate that the sodium layer temperature rises to a midwinter maximum (∼230 K) and then falls to a midsummer minimum (∼150 K), in qualitative agreement with the CIRA 1972 model predictions. Nightglow intensity measurements obtained with the interferometer indicate a highly variable behaviour, ranging from near-constant intensities, to monotonically falling, and to rising and falling intensities during the night. Broadening of the nightglow line profiles yields a sodium atom dissociation kinetic energy of (46 ± 4) meV. This suggests that the Chapman NaO + O chemiexcitation process, rather than dissociative recombination of “corkscrewing” ions and electrons, gives rise to the nightglow.

A Fabry-Perot interferometer has been used to determine equatorial thermospheric wind velocities from measurements of the doppler shifts in the twilight and nightglow 630.0 nm emission line observed from Kwajelein Atoll (9° 24′ N., 167° 29′ E.) during August and September 1977. Shortly after sunset, the F-region neutral winds typically are directed roughly eastward at velocities ranging from 50 to 120 m/sec. The velocity grows moderately in magnitude for several hours and then turns somewhat southward, sometimes decreasing in the late night (∼03 h local time) to small values (

A three-mode microwave afterglow apparatus has been used in conjunction with a high-speed grating spectrometer to study the variation with electron temperature of the recombination coefficient ..cap alpha.. (Xe/sub 2/ /sup +/) and of the Xe* excited states produced by dissociative recombination over the range 300 < or = T/sub e/ < or = 8000 K. At low electron temperatures, 300--700 K, ..cap alpha.. (Xe/sub 2/ /sup +/) varies approximately as T/sub e//sup -1///sup 3/, with a smooth transition to a approx.T/sub e//sup -0//sup .//sup 7/ variation at higher electron temperatures, 1300--7400 K. At T/sub e/ = T/sub +/ = T/sub n/ = 300 K, ..cap alpha.. (Xe/sub 2/ /sup +/) = (2.3 +- 0.2) x 10/sup -6/ cm/sup 3//sec, in agreement with earlier studies at room temperature. At thermal energy (300 K) Xe* excited states up to but not exceeding the energy of the Xe/sub 2/ /sup +/ ion in its ground electronic and vibrational state are observed. With microwave heating to T/sub e/ approx. 8000 K additional, higher-lying Xe* states (up to approx.0.6 eV above the Xe/sub 2/ /sup +/ ion ground state) are produced by the dissociative recombination process. (AIP)

Simultaneous measurements of neutral winds from the Doppler shifts of the 15867 K (630. nm) emission of the night sky have been made at two midlatitude stations separated by about 26° in longitude and less than 1° in latitude (39.8° N, 105.5°W and 40.13° N, 79.16°W). Comparison of the measured winds show strong local time correlation and negligible universal time correlation, in particular for meridional winds. This behavior is expected for the thermosphere for solar-minimum, magnetically quiet conditions, when the strongest pressure forces driving the winds are caused by insolation. The results also show the basic assumption of longitudinal or zonal averaging of two-dimensional thermospheric models to be correct for at least the 26° longitudinal separation between the two stations.

IT is shown that Orsini, et al's inference, from an analysis of Atmosphere Explorer data, that N/sub 2//sup +/ ions in vibrationally excited states exhibit dissociative recombination coefficients in excess of 10/sup -6/ cm/sup 3//sec is incorrect. From the theory of the dissociative recombination process, an upper limit of approx.10/sup -7/ cm/sup 3//sec is obtained for recombination by N/sub 2//sup +/ ions in a particular vibration state at F-region electron temperatures. Available laboratory data on dissociative recombination of simple ions support this conclusion. As a possible alternative for the apparent rapid loss of vibrationally excited ions in the F-region it is suggested that the reaction N/sub 2//sup +/+O..-->..N+NO/sup +/ may exhibit the necessary increase in reaction rate with vibrational excitation in the ions.

Interferometric observations of the 630.0 nm nightglow brightness at the equatorial station of Arequipa. Peru (16.2/sup 0/S, 71.4/sup 0/W geographic, 3.2/sup 0/S dip latitude) have revealed widespread areas of airglow depletion, with reductions in intensity as large as factors of 3 or 4. These depletions correlated closely with large increases of the equatorward (northward) wind and the 630.0 nm kinetic temperature. On occasion, the usually small meridonal wind reached a velocity of 100 m/s near 22/sup h/ LT lasting for 1 or 2 hours. The temperature increases of 10 K or more existed only in the poleward (southward) direction. Comparisons with modeling calculations suggest that this effect results from an upward movement of the ionosphere along the inclined magnetic field lines, driven by the equatorward neutral wind. The airglow column integrated emission rate is consequently decreased by the slower rate of formation and subsequent dissociative recombination of molecular oxygen ions within the higher F-layer. We conclude that the transient period of equatorward wind is a result of the passage of the midnight pressure bulge.

A drift-tube mass-spectrometer apparatus has been used to determine thermal-energy (300 K) charge transfer rate coefficients for reactions of the type R/sub a//sup ts2+/+R/sub b/..-->..R/sub a//sup +/+R/sub b//sup +asterisk/ and R/sub a//sup ts2+/+R/sub b/..-->..R/sub a//sup +/+R/sub b//sup ts2+/+e/sup -/ (transfer ionization), where R=He, Ne, Ar, Kr, and Xe. Rate coefficients for ions in the low-lying, metastable excited states (/sup 1/S and /sup 1/D) as well as the ground state (/sup 3/P) have been determined and, in some cases, deexcitation (quenching) coefficients for /sup 1/S and /sup 1/D ions have been measured. Reactions with an exoergicity ..delta..Eapprox.4 eV are found to be fast, approaching the limiting Langevin rate, while for ..delta..E 7 eV the rates fall off dramatically, in some cases dropping to the radiative value (approx.10/sup -14/ cm/sup 3//sec). The equilibrium constant for the three-body association reaction Xe/sup 2 +/+2 Ne arrow-right-left (Xe Ne)/sup 2 +/+Ne has been determined at 300 K.

Atomic collision processes occurring in mercury vapor are determined from microwave measurements of the electron density during the afterglow. The electrons are brought into thermal equilibrium with the gas by adding helium to the mercury vapor to act as a "recoil gas." Measurements of the ambipolar diffusion coefficient, ${D}_{a}$, of ${\mathrm{Hg}}^{+}$ ions and electrons in helium yield the value ${D}_{a}n=2.6\ifmmode\times\else\texttimes\fi{}{10}^{19}$ (${\mathrm{cm}}^{2}$/sec) (atoms/cc) at 290\ifmmode^\circ\else\textdegree\fi{}K. The corresponding value for ${\mathrm{Hg}}^{+}$ ions in mercury is ${D}_{a}n=3.6\ifmmode\times\else\texttimes\fi{}{10}^{17}$ at 350\ifmmode^\circ\else\textdegree\fi{}K. Conversion of the atomic mercury ions to molecular ions according to the reaction ${\mathrm{Hg}}^{+}$+Hg+He\ensuremath{\rightarrow}${\mathrm{Hg}}_{2}^{+}$+He occurs at the rate of 140 (${p}_{\mathrm{Hg}}\ifmmode\cdot\else\textperiodcentered\fi{}{p}_{\mathrm{He}}$) ${\mathrm{sec}}^{\ensuremath{-}1}$. The measured recombination coefficient of ${\mathrm{Hg}}_{2}^{+}$ ions with electrons is $\ensuremath{\alpha}=5.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ cc/sec at 400\ifmmode^\circ\else\textdegree\fi{}K. Studies of the ionization produced by the collisions of pairs of mercury metastable atoms yield the values ${D}_{m}n=1.5\ifmmode\times\else\texttimes\fi{}{10}^{18}$ (${\mathrm{cm}}^{2}$/sec) (atoms/cc) for the diffusion coefficient and ${\ensuremath{\sigma}}_{d}=8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ for the de-excitation cross section of $^{3}P_{2}$ metastables at 350\ifmmode^\circ\else\textdegree\fi{}K.

The skin depth in superconducting aluminum is calculated from the measured frequency dependence of the surface resistance through the Kronig-Kramers integral transforms. At absolute zero, it is found that the skin depth $\ensuremath{\delta}$ is independent of frequency at low frequencies but begins to increase at higher frequencies. The maximum rate of increase of $\ensuremath{\delta}$ occurs when the photon energy equals the gap energy, $h\ensuremath{\nu}=3.2k{T}_{c}={\mathcal{E}}_{g}$; at this point $\frac{\ensuremath{\delta}(h\ensuremath{\nu}={\mathcal{E}}_{g})}{\ensuremath{\delta}(h\ensuremath{\nu}=0)}\ensuremath{\approx}1.12$. The maximum value of $\ensuremath{\delta}$ occurs at $h\ensuremath{\nu}\ensuremath{\approx}4k{T}_{c}$. The superconducting penetration depth $\ensuremath{\lambda}$ [i.e., $\ensuremath{\delta}(h\ensuremath{\nu}=0)$] is found to vary approximately as $\ensuremath{\lambda}(t)=\ensuremath{\lambda}(0){(1\ensuremath{-}{t}^{4})}^{\ensuremath{-}\frac{1}{2}}$, with $\ensuremath{\lambda}(0)=5.15\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ cm and $t\ensuremath{\equiv}\frac{T}{{T}_{c}}$. The effects of changes in the skin depth have been eliminated from the determination of the energy gap by calculation of the real part of the complex conductivity, ${\ensuremath{\sigma}}_{r}$. The energy gap values deduced from the behavior of ${\ensuremath{\sigma}}_{r}$ differ only slightly from the results obtained directly from the surface resistance measurements.

The continuity equation for electrons in a decaying plasma is solved numerically in three dimensions including a loss term quadratic in the electron density (i.e., two-body electron-ion recombination) and an ambipolar diffusion term. The geometries investigated are the finite cylinder, the rectangular parallelepiped, and some one-dimensional cases. The electron densities are averaged assuming weighting functions corresponding to various microwave probing field distributions (cylindrical TM 010 , TE 011 , and TE 111 and retangular TE 101 modes) and are therefore directly proportional to measured quantities, such as resonant frequency shifts, obtained in microwave afterglow studies of recombination. Three different initial electron distributions are used, corresponding to a uniform (recombination controlled), a fundamental diffusion mode and a somewhat more spatially constricted distribution. The linear range of the computed (averaged densities) −1 -versus-time curves is determined and correction factors are derived which, if applied to the observations, yield the corrected recombination coefficients from the curves. The corrections derived in the two- and three-dimensional analyses are found to be significantly larger than those obtained in the one-dimensional analyses. Also, when considering plasma containers of different shapes but of the same fundamental diffusion length, a larger surface/volume ratio is found to be equivalent in effect to an increased diffusion coefficient in the predicted decays. In most cases of practical interest, though, a much stronger dependence upon the varying probing field distributions is found when different container or cavity dimensions are to be compared. When the present analysis is applied to one-dimensional geometries, recombination corrections in agreement with the results of Gray and Kerr are obtained.

Microwave techniques are applied to the study of the diffusion of electrons and positive ions in helium. For the electron and ion densities realized experimentally, the diffusion takes place ambipolarly; that is, the flow of charged particles of both signs is equalized by the space charge field which they set up. At 1 mm Hg pressure and 0.039-ev average energy, the measured value of the ambipolar diffusion coefficient, ${D}_{a}$, is 540 ${\mathrm{cm}}^{2}$/sec. The measured variation of ${D}_{a}$ with gas density, energy of the particles, and diffusion container size and shape agrees closely with theory.

A microwave-afterglow/mass-spectrometer apparatus which employs microwave heating of the electrons is used to determine the recombination coefficients, $\ensuremath{\alpha}({\mathrm{O}}_{2}^{+})$ and $\ensuremath{\alpha}({\mathrm{N}}_{2}^{+})$, of mass-identified ions with electrons as a function of electron temperature. From electron-density decay data taken under good "ion-tracking" conditions it is found that $\ensuremath{\alpha}({\mathrm{O}}_{2}^{+})$ varies as ${{T}_{e}}^{\ensuremath{-}0.70}$ over the range $300\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}l~{T}_{e}l~1200\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}$ [starting from a value (1.95 \ifmmode\pm\else\textpm\fi{} 0.2) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec at ${T}_{e}=300\ifmmode^\circ\else\textdegree\fi{}$K] and then varies as ${{T}_{e}}^{\ensuremath{-}0.56}$ between 1200 and 5000\ifmmode^\circ\else\textdegree\fi{}K. In the nitrogen studies the "ion tracking" of the electron decay is less perfect, but ${\mathrm{N}}_{2}^{+}$ remains the principal afterglow ion and $\ensuremath{\alpha}({\mathrm{N}}_{2}^{+})$ is found to vary as ${{T}_{e}}^{\ensuremath{-}0.39}$ over the entire range $300\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}l~{T}_{e}l~5000\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}$, starting from a value (${1.8}_{\ensuremath{-}0.2}^{+0.4}$) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec at ${T}_{e}=300\ifmmode^\circ\else\textdegree\fi{}$K. These results are compared with other laboratory determinations, results of theoretical calculations, and values inferred from analyses of ionospheric measurements.

Measurements of the temperature dependence of the microwave absorption in superconducting aluminum have been made in the wavelength region 20 mm to 3 mm. The results, when plotted as isotherms of surface resistance ratio vs photon energy, show that, at a well-defined energy for each temperature, there is a rapid rise in absorption with increasing energy. This has been interpreted as the onset of absorption resulting from direct excitation of electrons across a forbidden energy gap. The isotherms then permit the determination of the temperature dependence of this energy gap. At absolute zero the gap value is found to be ${\mathcal{E}}_{g}(0)=(3.2\ifmmode\pm\else\textpm\fi{}0.1)k{T}_{c}$ (where ${T}_{c}=1.178\ifmmode^\circ\else\textdegree\fi{}$K is the superconducting transition temperature), in reasonable agreement with the theoretical value of $3.52k{T}_{c}$ obtained by Bardeen, Cooper, and Schrieffer. Furthermore, the temperature variation of the gap exhibits the same shape as that given by the theory. Finally, reasonable agreement is obtained between theory and experiment concerning the detailed shapes of the surface resistance vs temperature curves over the measured wavelength range, provided that the experimental value ${\mathcal{E}}_{g}(0)$ is used in the theory.

A drift-tube\char22{}mass-spectrometer apparatus has been used to determine the mobilities of mass-identified atomic ions in the noble gases as a function of $\frac{E}{p}$ (drift field/gas pressure) at $T=295$ K. The measured values of the reduced mobilities ${\ensuremath{\mu}}_{0}$ of ${\mathrm{He}}^{+}$ in He, ${\mathrm{Ne}}^{+}$ in Ne, and ${\mathrm{Ar}}^{+}$ in Ar are in agreement with earlier investigations that did not employ mass identification. The measured value at $\frac{E}{p}=O$, ${\ensuremath{\mu}}_{0}({H}^{+} \mathrm{in}\mathrm{He})=({31.0}_{\ensuremath{-}1.0}^{+0.5})$ ${\mathrm{cm}}^{2}$ ${\mathrm{V}}^{\ensuremath{-}1}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, is in good agreement with quantum-mechanical calculations, but the observed decrease of ${\ensuremath{\mu}}_{0}$ with ion energy is somewhat slower than that predicted by theory. The measured mobility of each of the noble-gas ions ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$, ${\mathrm{Kr}}^{+}$, and ${\mathrm{Xe}}^{+}$ in He is found to be $\ensuremath{\sim}(6\ensuremath{-}12)%$ lower than that of the corresponding alkali-metal ion (as determined by Tyndall's group).

A method is described for measuring the mobilities of ions of near-thermal energy. A pulse of ions is generated in a discharge region and passes through a grid into a drift region where a uniform electric field causes the ions to move to a collector electrode. The mobilities are determined from measurements of the transit time of the ions in crossing the drift space. The experimental mobility values for thermal energy ions moving in their parent gases at 300\ifmmode^\circ\else\textdegree\fi{}K and a gas density of 2.69\ifmmode\times\else\texttimes\fi{}${10}^{19}$ atoms/cc are ${\ensuremath{\mu}}_{0}=10.5$ ${\mathrm{cm}}^{2}$/volt-sec (${\mathrm{He}}^{+}$), 20.3 (${\mathrm{He}}_{2}^{+}$), 4.0 (${\mathrm{Ne}}^{+}$), 6.5 (${\mathrm{Ne}}_{2}^{+}$), 1.60 (${\mathrm{A}}^{+}$), 2.65 (${\mathrm{A}}_{2}^{+}$), 0.90 (${\mathrm{Kr}}^{+}$), 1.21 (${\mathrm{Kr}}_{2}^{+}$), 0.58 (${\mathrm{Xe}}^{+}$), and 0.79 (${\mathrm{Xe}}_{2}^{+}$). These values are in good agreement with available theoretical results. Our measurements join smoothly at higher ion energies with the measurements made by Hornbeck and by Varney except in the case of ${\mathrm{A}}_{2}^{+}$. In addition, our results indicate that earlier measurements at near-thermal energy by Tyndall and collaborators refer to the molecular ions in helium and neon, and to the atomic ions in krypton and xenon.

Measurements of non-resonant charge transfer between atomic ions and atoms have been made in a drift tube/mass spectrometer apparatus as a function of E/p (drift field/gas pressure) at 295 K. Comparison of the measured rates with available theories suggests an inability to predict the moderately slow reaction rates.

Microwave, optical spectrometric, and interferometric techniques have been used to investigate the nature of the electron-ion recombination process in low-pressure, pure helium afterglows at 300 and 77\ifmmode^\circ\else\textdegree\fi{}K. To determine whether dissociative capture of electrons by helium molecular ions, i.e., ${{\mathrm{He}}_{2}}^{+}+e\ensuremath{\rightarrow}{\mathrm{He}}^{*}+\mathrm{He}+(\mathrm{KE})$, is the recombination reaction taking place, we have attempted to detect the kinetic energy of dissociation of the excited atoms produced in the recombination process by a study of the widths of the emitted afterglow lines. A model of the low-pressure helium afterglow which reasonably accounts for our electron density, line intensity, and linewidth observations involves principally the creation of ${\mathrm{He}}^{+}$ ions and electrons by the collisions of pairs of helium metastable atoms, the three-body conversion of ${\mathrm{He}}^{+}$ ions to ${\mathrm{He}}_{2}^{+}$ ions, the ambipolar diffusion of ${\mathrm{He}}^{+}$, ${\mathrm{He}}_{2}^{+}$, and electrons, and the diffusion of helium metastable atoms to the walls. The $\ensuremath{\lambda}5876$ radiation ($3^{3}D\ensuremath{-}2^{3}P$ transition) from the later part of the afterglow, when recombination of ${\mathrm{He}}_{2}^{+}$ and electrons is expected to be the source of the excited atoms, exhibits a substantial broadening over the approximately thermal width observed during the discharge and in the early afterglow, when the radiation is expected to originate from electron impact excitation of helium atoms. It is concluded that the dissociative recombination process is the likely source of the observed afterglow line broadening.

Microwave techniques are applied to the measurement of the recombination between electrons and positive ions. The measured recombination coefficients for monatomic gases range from 1.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ cc/ion-sec. for helium to 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ cc/ion-sec. for argon. The recombination coefficients for diatomic gases range from 2.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ cc/ion-sec. for hydrogen to 2.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ cc/ion-sec. for oxygen. At electron temperatures of 300\ifmmode^\circ\else\textdegree\fi{}K, the recombination is found to be independent of pressure for the monatomic gases. A pressure dependence is observed in diatomic gases, the recombination increasing with increasing pressure in nitrogen and oxygen.

The mobilities of ions of near thermal energies are measured in helium-neon mixtures using a drift velocity apparatus. These studies permit the investigation of ion motion in gases, e.g., ${\mathrm{He}}^{+}$ in Ne, under conditions where the charge transfer interaction is negligible compared to polarization attraction and short-range repulsion between ion and atom. In addition, the measurements provide a test of Blanc's empirical law, $\frac{1}{\ensuremath{\mu}}=\frac{{f}_{1}}{{\ensuremath{\mu}}_{1}}+\frac{{f}_{2}}{{\ensuremath{\mu}}_{2}}$, which relates the mobility $\ensuremath{\mu}$ in a binary mixture to the pure gas mobilities ${\ensuremath{\mu}}_{1}$ and ${\ensuremath{\mu}}_{2}$ and to the fractional gas concentrations ${f}_{1}$ and ${f}_{2}$. A theoretical treatment developed by Holstein is presented which shows that deviations from Blanc's law are limited to a few percent. The mobilities of ${\mathrm{He}}^{+}$, ${\mathrm{He}}_{2}^{+}$, and ${\mathrm{Ne}}_{2}^{+}$ ions are found to obey accurately Blanc's law. However, the "${\mathrm{Ne}}^{+}$" ion curve deviates markedly from the law. These deviations are explained in terms of the formation of moderately stable ${(\mathrm{He}\mathrm{Ne})}^{+}$ ions from ${\mathrm{Ne}}^{+}$. Finally, the observed mobilities of ${\mathrm{He}}_{2}^{+}$ in Ne and ${\mathrm{Ne}}_{2}^{+}$ in He are found to agree with the predictions of polarization theory.

The temperature dependence of the coefficient for the recombination of electrons with mass-identified ${\mathrm{O}}_{2}^{+}$ ions has been determined from observations of the electron and ion decay rates in the afterglow following "single-pulse" microwave discharges in ${\mathrm{O}}_{2}$-Ne, ${\mathrm{O}}_{2}$-Ne-Ar, and ${\mathrm{O}}_{2}$-Ne-Kr gas mixtures. Temporal mass analysis, utilizing multichannel signal-averaging techniques, shows similar decay rates for the electrons and for the ${\mathrm{O}}_{2}^{+}$ ions over the major portion of the afterglow. The observed recombination coefficient, $\ensuremath{\alpha}({{\mathrm{O}}_{2}}^{+})$, has a temperature dependence approximated by ${{T}_{\mathrm{gas}}}^{\ensuremath{-}1}$, the values at temperatures of 205, 295, and 690\ifmmode^\circ\else\textdegree\fi{}K being (3.0\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$, (2.2\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$, and (1.0\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec, respectively. At the lower temperatures the dimer ion ${\mathrm{O}}_{2}$ \ifmmode\cdot\else\textperiodcentered\fi{} ${\mathrm{O}}_{2}^{+}$ becomes significantly more important. Analysis of the data yields a coefficient of approximately 2.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{3}$/sec for the recombination of this ion with electrons at a temperature of 205\ifmmode^\circ\else\textdegree\fi{}K.

A pressure-tuned Fabry-Perot interferometer employing photoelectric detection has been used to measure the oxygen λ 6300 and λ 5577 spectral line profiles during twilight and the night at the Airglow Observatory on Laurel Mountain, Pennsylvania. The infrared O ( 1 D) atom temperatures, ranging from ∼600–1600°K, are compared with the predicted temperature variations using empirical models relating solar activity to exospheric heating, and agreement is found on some nights, while substantial discrepancies (∼400°K) are found on others. No evidence for or against a dissociative origin of the 1 D or 1 S oxygen atoms has been obtained from the line profiles observed to date, probably owing to rapid thermalization of any such excited atoms before radiation can occur. However, there is a possible indication of F -layer wind velocities of ∼400m/s.

Spectral line profiles on neon and argon determined by high resolution, photoelectric recording, pressure tuned Fabry-Perot interferometer

Photo-ionized plasma afterglows of NO have been studied by combined microwave and mass-spectrometric techniques. Nitric-oxide-neon mixtures (5-65 mTorr NO, 2-7 Torr Ne) are contained in a 10-cm resonant cavity where they are ionized by a "single pulse" of Lyman-$\ensuremath{\alpha}$ radiation. A temporal spectrum of ions diffusing to the wall is obtained by a differentially pumped mass spectrometer and multichannel analyzer. Analysis of the electron-density decay curves obtained by microwave techniques to obtain an electron-ion recombination coefficient for N${\mathrm{O}}^{+}$ is complicated by the conversion of N${\mathrm{O}}^{+}$ to the dimer ion, ${(\mathrm{NO})}_{2}^{+}$. At sufficiently low densities of nitric oxide the ${(\mathrm{NO})}_{2}^{+}$ concentration becomes negligible, and the N${\mathrm{O}}^{+}$ wall current tracks the electron-density decay. From comparisons of experimental electron-density decay curves obtained under recombination-controlled conditions, with computer solutions of the electron-continuity equation, the values $\ensuremath{\alpha}(\mathrm{N}{\mathrm{O}}^{+})=(7.4\ifmmode\pm\else\textpm\fi{}0.7), (4.1\ifmmode\pm\else\textpm\fi{}{0.3}{0.2}), \mathrm{and} (3.1\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec, at $T=200, 300, \mathrm{and} 450\ifmmode^\circ\else\textdegree\fi{}$K, respectively, are obtained. From analysis of electron-density decay curves at higher densities of NO, where ${(\mathrm{NO})}_{2}^{+}$ is the dominant ion, the value $\ensuremath{\alpha}{{(\mathrm{NO})}_{2}}^{+}=(1.7\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{3}$/sec at $T=300\ifmmode^\circ\else\textdegree\fi{}$K is obtained. The three-body electron-attachment and ambipolar diffusion coefficients have been measured in pure NO (0.1-5 Torr) and are found to be $K=(1.3\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}31}$ ${\mathrm{cm}}^{6}$/sec and ${D}_{a}p=80\ifmmode\pm\else\textpm\fi{}16$ ${\mathrm{cm}}^{2}$ Torr/sec, respectively, at $T=300\ifmmode^\circ\else\textdegree\fi{}$K.

A direct recording Fabry‐Perot interferometer is described which has a high optical speed and provides a direct tracing of spectral line shapes on a linear scale. A photomultiplier views the center spot of the interference pattern. The output of the photomultiplier goes to a vibrating‐reed electrometer and then to a pen recorder. The wavelength of the light at the center of the interference pattern is made to vary with time by changing the index of refraction between the interferometer plates. This is accomplished by enclosing the plates in a gas‐tight housing and admitting an inert gas such as argon or helium to the housing. By the proper choice of gas and of the rate of pressure change, one obtains the desired rate of tracing the line shape. Orders of magnitude reduction in ``exposure'' time are achieved by eliminating the use of photographic plates.

Use of Fabry-Perot interferometer measurements of atomic-oxygen 6300- and 5577-A line profiles from twilight and nightglow to determine the neutral temperatures in the F2 and E regions of the earth's ionosphere. The exospheric temperatures determined from the 6300-A profiles are usually somewhat higher than the temperatures calculated from Jacchia's model, and differences as large as about 300 K are noted when the exospheric temperature equals 1500 to 1600 K. The postsunset and predawn rate of change of the exospheric temperature is often substantially larger than the Jacchia prediction. The 5577-A (E region) measured temperatures range from 200 to 220 K on quiet nights to 500 to 600 K during geomagnetic storms.

Mobilities of singly and doubly charged ions of neon, argon, krypton, and xenon in helium and of xenon in neon have been determined in a drift-tube mass-spectrometer apparatus at temperatures near 300 K and for $10\ensuremath{\le}\frac{E}{N}\ensuremath{\le}100$ Td. The zero-field reduced mobility of a given doubly charged ion is found to be either equal to or slightly smaller than that of its singly charged counterpart. However, the dependences of the mobilities on $\frac{E}{N}$ are found to be strikingly different for the two cases. No difference in mobility is observed between doubly charged ions in the low-lying, metastable states and in their ground state, in contrast to the case of the ions drifting in their parent gases.

Microwave techniques are used to study electron attachment to iodine molecules during the afterglow following a pulsed discharge in an iodine-helium mixture. The helium gas decreases the ambipolar diffusion loss of the electrons and assures that the electrons are in thermal equilibrium with the gas during the afterglow. It is shown that under the experimental conditions electron attachment is the dominant electron-loss process. The measured cross section for electron attachment to iodine at 300\ifmmode^\circ\else\textdegree\fi{}K is ${\ensuremath{\sigma}}_{a}=3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$.

The mobilities of mercury ions in helium, neon, and argon have been measured at 300\ifmmode^\circ\else\textdegree\fi{}K. The values obtained are ${\ensuremath{\mu}}_{0}=19.6(\mathrm{He}), 5.95 (\mathrm{Ne}), \mathrm{and} 1.84 (\mathrm{A})$ ${\mathrm{cm}}^{2}$/volt-sec. These values are in agreement with extrapolations of the mobility versus mass-number curves obtained for alkali ions in the noble gases by Tyndall and collaborators. The experimental values for ${\mathrm{Hg}}^{+}$ are compared with the Langevin theory in the polarization limit. Good agreement is obtained only for the case of argon.