A. L. Schmeltekopf's research while affiliated with University of Colorado Boulder and other places
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Publications (122)
We describe a near-infrared in situ tunable diode laser spectrometer developed for atmospheric measurements of CH4 in the upper troposphere and lower stratosphere (UT/LS). The instrument is designed to provide fast-response (0.5–1Hz) measurements
and operate autonomously on the NASA WB-57F high-altitude aircraft. A single-mode InGaAsP distributed f...
Daytime positive ion densities calculated using recently measured laboratory ion-neutral reaction rate constants are compared with the NRL rocket results between 120 and 220 km. The calculated O+ and N-2(+) densities are found to be in good agreement with the ionospheric observations. The main N-2(+) loss process in this region is the reaction N-2(...
The Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE) made in situ observations of the composition of the lower stratosphere from the NASA ER-2 aircraft at latitudes from 15°N to 60°N, during November 1992 and April, May and October 1993. SPADE followed the Airborne Arctic Stratospheric Expedition II (AASW-II, September 1991...
Ground-based measurements of NO3 absorption in the band near 662 nm were carried out on four occasions using the moon as a light source during sunrise at both middle and polar latitudes. As the sun rose, the observed slant column abundance of atmospheric NO3 decreased systematically. The observed time dependent decrease is due to the progression of...
The first spectroscopic measurements of chlorine dioxide throughout Antarctic fall, winter, and spring were carried out at McMurdo Station during April to October 1991. Two different observing modes were employed to extend the measurements over the broadest possible seasonal range: direct Moon measurements were used as well as observations of the s...
Lunar absorption spectra have been used to determine the vertical column abundances of NO[sub 2] and NO[sub 3] above McMurdo Station, Antarctica (77.8[degrees]S), during the fall, winter, and spring seasons in 1991. The observed nighttime NO[sub 2] and NO[sub 3] amounts during the fall and spring were broadly consistent with model predictions and w...
Studies have indicated that, with sufficient technology development, high speed civil transport aircraft could be economically competitive with long haul subsonic aircraft. However, uncertainty about atmospheric pollution, along with community noise and sonic boom, continues to be a major concern; and this is addressed in the planned 6 yr HSRP begu...
In situ ozone measurements were made from the ER-2 aircraft during the 1987 Airborne Antarctic Ozone Experiment both inside and outside the ozone hole. Midday measurements from late August until late September during aircraft ascent near 53 deg S latitude indicate no clear temporal trend in ozone mixing ratio but instead reflect the distance of the...
Measurements of the abundances of ozone over Antarctica in August and September 1987 obtained during the Airborne Antarctic Ozone Experiment are intercompared. These measurements of ozone concentrations and total column abundance were obtained by three satellite instruments, two IR and one UV column-measuring instruments aboard the DC-8, one in sit...
A sensitive absorption spectrograph was flown on the NASA DC-8 aircraft as part of the 1987 Airborne Antarctic Ozone Experiment to measure column abundances of O3, NO2, OClO, and BrO inside the Antarctic polar vortex. The instrument functioned successfully on all flights. Slant column NO2 measurements were made every 300 s whenever light levels per...
Observations of the evening twilight BrO abundance over McMurdo Station, Antarctica during austral spring, 1987, are described. The observed variation of the slant column abundance with increasing solar zenith angles suggests that most of the BrO is located near 15 km. The total vertical column abundance observed during one week of measurements yie...
Stratospheric NOâ is expected to depend strongly upon two major factors: solar illumination and temperature. This paper presents observations in the polar regions that confirm the influence of both of these on the NOâ column abundance. Measurements of the absorption of incoming lunar radiation near 662 nm as the sun rises exhibit large changes that...
Laboratory measurements of the near-ultraviolet spectra of O3, NO2, and OClO as a function of temperature are presented. Comparisons are made with observed features in sky spectra. The ratios between measured slant column abundances reveal that the O3 and OClO column abundances are centered in the lower stratosphere, near 20 km, while that of NO2 i...
Observations of the diurnal variations of OClO and BrO during austral
spring, 1987, using long-path visible and near-ultraviolet absorption
spectroscopy are presented and compared to simplified model
calculations. It is shown that care must be taken to compare model
calculations and measurements along the line of sight of the instrument.
Evening tw...
The daytime and nighttime slant column abundances of OClO were measured by near-UV absorption spectroscopy between 64 and 76 deg S latitude and 62 and 84 deg W longitude during the DC-8 flight on days 251 and 252 (UT) 1987 as a part of the Airborne Antarctic Ozone Experiment (AAOE). Daytime and nighttime measurements used the scattered sunlight and...
Observations at Thule, Greenland, that made use of direct light from the moon on 2,3, 4,5, and 7 February 1988 revealed nighttime
chlorine dioxide (OClO) abundances that were less than those obtained in Antarctica by about a factor of 5, but that exceeded
model predictions based on homogeneous (gas-phase) photochemistry by about a factor of 10. The...
Scattered sunlight and direct light from the moon was used in two wavelength ranges to measure the total column abundances of stratospheric ozone(O(3)) and nitrogen dioxide (NO(2)) at Thule, Greenland (76.5 degrees N), during the period from 29 January to 16 February 1988. The observed O(3) column varied between about 325 and 400 Dobson units, and...
Simultaneous in situ measurements of NO, NO2, and O3 were obtained from balloon flights near 50 deg N in August and December 1982. NO(x)(NO + NO2) was reduced by a factor of 10 in the 21- to 28-km region in winter. Both NO and NO2 exhibited very sharp vertical gradients in the vicinity of 29 km. NO, for example, increased by nearly 20 times over on...
An observing program aimed at obtaining visible light spectra at McMurdo Station, Antarctica, during austral spring in 1986 is described. Total ozone abundances in late August within the polar vortex were of the order of 275 DU, suggesting that the bulk of the ozone column depletion had not yet occurred. That depletion occurred mainly during Septem...
The total column abundance of NO3 was measured in Antarctica during the nights of Sept. 17-19, 1986, by visible absorption, using the moon as the light source. The variation of the observed abundance with lunar zenith angle suggests that the bulk of the layer is located in the stratosphere. In agreement with theoretical model calculations, the tota...
The column abundance of OClO at McMurdo Station, Antarctica, was measured by visible absorption spectroscopy during austral spring in 1986. Observations were obtained during the day using scattered sunlight and at night using direct light from the moon. The observed total column amounts in Antarctica were about 20-50 times larger than would be expe...
Observations of the visible spectra of the sun and moon were obtained at McMurdo Station, Antarctica, during austral spring in 1986. The data coverage and observing conditions are described. Daily variations of ozone suggest that the bulk of the springtime ozone depletion (or the Antarctic ozone 'hole') occurs rapidly during early September. Total...
Observations of several atmospheric species can be performed by
measuring the absorption of visible and near-ultraviolet light scattered
from the zenith sky. The determination of vertical column abundances of
molecules such as ozone and NO2 from such measurements is briefly
reviewed. It is shown that the conversion of NO to NO2 can be of
significan...
Laboratory and field studies have been carried out to determine the equilibrium constant for the system, N2O5 yields reversibly NO3 + NO2. In the laboratory studies a 170-m multiple-pass cell was used to study the equilibrium with the reactants at the ppm level in 700 torrs N2/O2 near 298 K. A Fourier transform infrared spectrometer was employed to...
The A2Σ+ → X2Π band system of OT was observed for the first time. Fourteen bands with 0 ≤ v′ ≤ 4 and 0 ≤ v″ ≤ 3 were photographed at high resolution and rotationally assigned. Fitted values of 18 effective parameters of the model Hamiltonians used to describe individual vibrational levels of the two states are determined by least-squares from the d...
Total water was measured in the high troposphere and low stratosphere over Panama during ten aircraft flights. The results show that convective storms provide the means of transporting water into the stratosphere. From a consideration of the anvil heights over different areas of the tropical zone, it follows that a negative gradient of water vapor...
All of our previously published atmospheric N2O mixing ratio data must be divided by 1.07 to correct for an error that we have recently discovered in our 1975 N2O primary standard. This problem was uncovered during intercomparison of our electron-capture, gas-chromatographic measurement technique for N2O with a newly developed infrared absorption t...
Some recent results on the measurement of the mixing ratio of stratospheric water vapor are reported. The instrument uses photodissociation of water followed by fluorescence of the hydroxyl fragment (PFF). This instrument has a large signal to noise ratio at integration times of 1 second, so that potential structure and fine structure of the water...
The mixing ratios of CFCl3, CF2Cl2, and N2O have been measured as a function of altitude from 6 to 37 km above sea level by using a balloon-borne grab-sampling system. The 24 flights were made during the period July 1976 to March 1979 from Wyoming, Panama, Brazil, and Antarctica. These data are reported here both numerically and graphically, the la...
The results of four balloon flights of the NOAA ultraviolet fluorescence
stratospheric water vapor instrument are presented. A series of
improvements in the instrument has brought results which are credibly
free from contamination by outgassing. The results are in essential
agreement with the extensive soundings by H.J. Mastenbrook. The minimum
wat...
In recent years, high‐resolution photoelectron spectroscopy and ab initio calculations have considerably revised and enlarged the understanding of the electronic structure of the NO+ ion. Based on these results, new potential energy curves for the electronic states of NO+ below 24 eV have been constructed and are given here. RKR potentials were cal...
Surface nitric oxide mixing ratios were measured in the equatorial Pacific region using a chemiluminescent detector. The average NO mixing ratio was about 4 parts per trillion by volume during noontime conditions for nine days of measurements. These NO mixing ratios, which are much lower than any previously reported, imply that the O3 production ra...
Samples of stratospheric air were obtained at altitudes up to about 35 km from balloon flights carried out at 4 deg S (Brazil), 78 deg S (Antarctica), and 41 deg N (two flights, Wyoming) in 1978. The samples obtained were analyzed for methane using a gas chromatograph with flame ionization detection. The two Wyoming profiles and the Antarctica prof...
Absolute rate constants are reported for the deactivation of O(1D) by five trace atmospheric constituents for the temperature range 200–350 K. O(1D) atoms produced by photolyzing ozone with a frequency quadrupled pulse from a Nd-YAG laser are monitored directly by means of the O(1D) ↠O(3P) emission at 630 nm. All the gases studied here are thought...
The flowing afterglow and flow-draft instrumental laboratory
capabilities have been applied during the past year to the experimental
investigation of the kinetics and thermochemistry of important D-region
atomic and molecular ions. The information obtained will be used to
redefine the atmospheric ionic composition and the processes by which
this io...
The O 2+b
4Σg--a
4Πu First Negative band system has been
extended to the v = 3 level of the upper state by photographing the (3,
1) band in high resolution. This and other newly recorded bands and the
previously measured bands of this system have been reduced to molecular
constants using a method to merge the least-squares results of separate
band-...
A method is presented for merging the results of separate least-squares fits to obtain the most precise, single values for each of the molecular constants of a spectroscopic system. The output molecular constants and accompanying variance-covariance matrices from each of the separate fits are taken together as input to a correlated least-squares fi...
A number of N2O profiles obtained in the troposphere and stratosphere at
five latitudes are reported. The variability in the reported
stratospheric N2O mixing ratios is substantial and indicates a strong
dependence on both stratospheric transport and photochemistry. A profile
obtained at Panama indicates a relatively large transport of N2O into
the...
A lightweight balloon‐borne grab‐sampling system for determining mixing ratios ≪10<sup>-9</sup> of chlorocarbons and other minor constituents in the stratosphere is described. The all‐metal system consists of five sampling spheres and associated valves, which are opened and closed at selected altitudes by on‐board electronics during a parachute des...
Absolute rate constants and their temperature dependencies for the deactivation of O(1D) by five important atmospheric gases are reported. O(1D) atoms are produced by photolysis of ozone at 266 nm and the atoms are directly observed in time resolved decay of the O(1D) ↠O(3P) radiation at 630 nm. Gases which only quench O(1D) (O2, N2, and CO2) are o...
The possibility of significant losses of chlorofluoromethanes and their
photochemical products in the troposphere or stratosphere has been
examined. A number of laboratory measurements have been carried out
involving possible ambient positive and negative ions and
CFCL3, CF2Cl2 and HCl. No reactions
between ions expected to have significant concent...
Absolute rate constants for the deactivation of O(1D) atoms by some
atmospheric gases have been determined by observing the time-resolved
emission of O(1D) at 630 nm. O(1D) atoms were produced by the
dissociation of ozone via repetitive laser pulses at 266 nm. Absolute
rate constants for the relaxation of O(1D) at 298 K are reported for N2,
O2, CO2...
The $A^{2}\Sigma^{+} - X^{2}\Pi_{i}$ band system of OT has been photographed in high resolution. Nonlinear least-squares fits of $^{2}\Sigma$ and $^{2}\Pi$ Hamiltonians have been made to each of the observed fourteen bands. Particular attention was given to determining the constants representing the various centrifugal distortion interactions. The...
The ion chemistry of HNO3 is studied at 298 °K. The attachment of thermal electrons to HNO3 to produce NO−2 is found to have a rate constant of (5±3) ×10−8 cm3/sec. HNO3 reacts rapidly (k∼10−9 cm3/sec) with a large variety of negative ions including Cl−, NO2−, O2−, and CO−3. HNO3 is also found to bond strongly to NO3−. The proton affinity of HNO3 i...
The forward and reverse rate constants for the proton-transfer reaction, N2OH++CO?COH++N2O, have been measured as a function of temperature in a variable-temperature flowing afterglow and as a function of relative kinetic energy in a flow-drift tube using both helium and argon buffer gases. The temperature variation of the rate constant was used to...
Stratospheric air samples have been obtained at 17.7, 22.3, and 26.2 km using balloon borne sampling spheres launched from Laramie, Wyo. These samples have been analyzed for CFCl3, CF2Cl2 and N2O, using electron capture detector gas chromatography. The concentrations of all three constituents are compared with theoretical models and found to be in...
Rate constants for the reaction of O+2(a 4&Pgr;u) metastable ions with N2, Ar, CO, CO2, H2, and O2, which do not react with O+2(X 2&Pgr;g, v=0) ground-state ions, have been measured for the relative kinetic energies 0.04–2 eV in a flow-drift tube. With the exception of O2 and CO, most of the rate constants are near the respective Langevin limits. T...
The rate constants for several exothermic proton-transfer reactions have been measured as a function of relative ion kinetic energy in a flow-drift tube. The reactions include the exothermic proton transfers of O2H(+) with N2, CO2, and NH3, H3(+), CH5(+), COH(+), and NH3(+) with NH3. The energy range covered is from thermal to about an electron vol...
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made. Most of these measurements have been carried out at room temperature (300øK). The F region of the terrestrial ionosphere has temperatures exceeding 1000øK or even 2000øK at solar maximum conditions, and it is important for ionospheric analysis that the reaction rate constants be known at the appropriate temperature. No quantitative theory ha...
Reaction rate constants for the quenching of the 23S state of helium by Ne, Ar, Xe, H2, N2, O2, CO2, and NH3 have been measured as a function of temperature between 300 and 900°K in a flowing afterglow. All of these rate constants increased with temperature. This finding offers an explanation for the discrepancies among recently published values fo...
The use of helium metastables in the NOAA flowing afterglow experiment was discussed. Measurements of de-excitation rate constants made in this system were described (1) and the long-standing experimental disagreement (2) between the afterglow results and those from beam measurements was discussed. New flowing-afterglow measurements made in a tempe...
The important ionospheric reaction (1)(2) has been measured from thermal energy (300°K) to ∼1 eV relative kinetic energy in a flow-drift tube experiment. The results can be summarized as follows: k1 = (1.4±0.7) × 10−10(T/300)−0.44 cm³/s when T < 1500°K, k1 = (5.2±2) × 10−11 (T/300)0.20 cm³/s when T > 1500°K, and k1a/k1 = 0.07(T/300)0.21. The result...
The energy dependence of the exothermic charge transfer reaction of O+ with NO, which is known to be anomalously slow at thermal energies, has been investigated with a new flow-drift tube apparatus. With increasing O+ kinetic energy in the center of mass the rate constant increases from an upper limit of 8 × 10−13 cm³ s−1 at thermal energy to 2 × 1...
The $O_{2}^{+}$ $b^{4}\sum_{g}$- - $a^{4}\Pi_{u}$ First Negative system has been extended to a new level of the upper state with the measurement of the (3,1) band. This new band and the previously measured bands of this system have been reduced to molecular constants by fitting each band separately and these results have been combined to yield a mi...
The positive ion-molecule reactions N++O2↠ NO++O↠ O2++N,N2++O2↠ O2++N2,O++O2↠ O2++O,O++N2↠ NO++N, were measured in a newly constructed flow-drift tube apparatus. Reactions (a), (b), and (c) were measured from thermal energy to approximately 2 eV ion kinetic energy in the center of mass. Reaction (d) was measured from 0.3–3 eV ion kinetic energy. Th...
The present paper describes the construction and operation of a new experimental device that combines the chemical versatility of a conventional flowing afterglow system with the energy variability of a drift tube. This allows the measurement of both positive and negative ion mobilities not previously measured. Ion mobility measurements offer a sig...
A new combined flowing afterglow‐drift tube experimental appartus has been used to measure the reaction rate constants as a function of ion kinetic energy for the following negative ion reactions: O − + CO → CO 2 +e, O − + NO → NO 2 +e, O − + H 2 → H 2 O +e → OH − H , O − + D 2 → D 2 O +e → OD − +D. Reaction (1) has been measured from thermal energ...
The derivation of explicit expressions for the Hund's case (a) matrix elements of R2k is discussed, where R is the mechanical rotational angular momentum operator of the molecule. A recursion relation is developed that permits matrix elements of R2k to be expressed in terms of those of R2(k-1), thus affording a straightforward means of calculating...
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A nonlinear fitting procedure is presented that employs all measured line positions and iteratively compares their values with those calculated from numerically diagonalized model Hamiltonians with adjustable molecular constants. Case (a) wavefunctions with definite parity are introduced as a convenient basis set, and the effects of spin-orbit, spi...
The discrepancies concerning the optical and microwave values of B0 and D0 for the X3Sigmag- state of O2 have been removed by a nonlinear least-squares fit to all of the lines of the O2, b 1Sigmag+-X 3Sigmag- Red Atmospheric bands recorded by Babcock and Herzberg (Astrophys. J., 108, 167, 1948). The resulting values for B0'' and D0'' are in excelle...
Two alternative methods for the reduction of observed line positions to spectroscopic constants are compared. In the direct approach, the line positions are fit directly to expressions for the energy level differences in which the upper and lower state molecular constants enter as unknowns. In the traditional term value approach, a two-step procedu...
Expressions are developed for computing the centrifugal distortion constants Dv, Hv, and Lv directly from the Rydberg-Klein-Rees rotationless potential of a diatomic molecule. These expressions involve summations over integrals of the wavefunctions of all neighboring vibrational levels. Application is made to the X1Sigma+ state of CO and the X3Sigm...
Existing high-resolution data for the Second Negative band system have been analyzed using a nonlinear least-squares fit that employs numerically diagonalized Hamiltonians. Values for the full set of molecular constants of the A2Πu and X2Πg states are obtained for the first time. In addition to values for ν0(v′, v″), Bv, and Dv, the values for the...
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Rate constants for collisional detachment of NO−, NO− + X ↠ NO + X + e, have been measured from 193 to 506°K for X as He, Ne, H2, NO, CO, CO2, N2O, and NH3. The data fit Arrhenius plots kd=Ae−E∕kT with both A and E showing large variations with X. From equilibrium constant considerations, electron attachment rates to NO have been calculated. An est...
Molecular constants can be determined from spectral data by (a) fitting the observed line positions with a set of calculated line positions given by the differences between the eigenvalues of numerically diagonalized Hamiltonians for the upper and lower states, and by (b) fitting the observed lines with a set of calculated term values and then subs...
The production of the O 2+(A 2Π
u), HBr +(A 2Σ +), and
HCl +(A 2Σ +) states from Penning
ionization by He(2 3S I) metastables was observed
to be a nonvertical process. The O 2+(A
2Π u) state shows high rotational excitation.
The association of NO+ with CO2, NO++CO2+He↠NO+·CO2+He, is found to occur with a rate constant 1 × 10−29 cm6 sec−1 at 197°K, decreasing at higher temperatures. When N2 or Ar are used as the third body the rate constant is about 3 times larger. The association of NO+ with O2 and N2 was found to be very much less efficient. It was found that NO+·CO2...
Employing the recent measurements of CO laser spectra and other precision absorption and emission data pertaining to this molecule, the RKR potential for the ${X}^{1}\Sigma^{1}$ state of the CO molecule was evaluated by two different approaches. The $r_{\max}$ and $r_{\min}$ values calculated agreed almost perfectly in these two sets of evaluations...
The de-excitation rate constants for He(21S) and He(23S) metastables have been measured with the following gases: Ne, Ar, Kr, Xe, H2, D2, N2, CO, NO, O2, CO2, NO2, NH3, SF6, CH4, C2H6, C3H8, and C4H10. These rate constants were measured in a flowing afterglow system using the neon 5689.8 and 7032.4-Å emission lines as detectors for the He(21S) and...
This chapter describes the experimental and analytical techniques that have been developed for flowing afterglow applications to the quantitative study of ion–neutral reaction processes. Most other techniques for the measurement of ion–molecule reaction rate constants are inherently unsuited for the examination of an ion reacting with a neutral whe...
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The application of a flowing afterglow technique to the measurement of thermal energy ion-molecule reactions is briefly discussed. The flowing afterglow system has the advantage of producing reactant species in their ground electronic and vibrational states in many cases and, additionally, allows the measurement of reactions of ions with unstable n...
From a He-beam excited by electron impact we eliminated the He(21S) component to better than 0.5% by irradiating light from a He discharge. The quenching process is hv(21P→21S)+He(21S)→He(21P)→He(11S +hv) (21P 1)1S. By measuring the ions produced in collisions of the He-metastables with various target gases in a mass spectrometer, singlet to triple...
The flowing afterglow technique for ion‐neutral reaction rate constant studies has been modified to cover a range of gas temperature from 82° to 600°K. The experimental apparatus is described and rate constants for six reactions between 300° and 600°K are reported. The reaction of He+ with N2 is found to have a rate constant 1.2 × 10−9 cm/3sec, ind...
The following reactions have been measured as a function of N2 vibrational temperature from 300°K to 6000°K: Chemical equation presented Reactions (1) and (3) are the first ion-molecule reactions to be measured as a function of vibrational temperature of the neutral. The rate constants for Reactions (1) and (2) are found to be insensitive to the N...
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Rate constants for reactions in which the positive ions O+, N+, Ar+, N2+, CO+, CO2+, and N2O+ abstract a hydrogen atom from H2 have been measured at 300°K in a pulsed, flowing‐afterglow reaction tube. Several additional reactions are observed which occur as secondary reactions in these experiments.
Laboratory experiments show that the ion-atom interchange reaction (1) has an increased rate constant when the N2 is vibrationally excited. For a Boltzmann distribution of N2 vibrational states such that Tv = 4000°K, the rate constant for (1) is increased by a factor of about twenty over the rate constant for ground vibrational state N2. This has i...
Rate constants for the loss processes of negative oxygen ions in the D-region of the ionosphere have been measured in the laboratory for the first time. Associative detachment reactions for O- and O2- ions with atomic oxygen dominate the loss of these ions when the atomic oxygen concentration exceeds the ozone concentration. When the ozone concentr...
A number of reactions that might be important in the martian ionosphere have been studied and their rate coefficients have been measured with a pulsed flowing afterglow system. One of the most important of these is O+ + CO2 → O2+ + CO, which has a rate coefficient of about 10-9 cm+3 sec-1. The ion chemistry is discussed and model ionospheres are co...