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Erdman, P. W.

Publications and source records attributed to Erdman, P. W..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Excitation of the OI (3s 5S0-3p 5P; lambda 7774 A) multiplet by electron impact on O2

Electron impact on O2 has been employed to ascertain the absolute cross-section value and emission linewidths of the OI (3s 5S0-3p 5P; 7774 A) multiplet. The emission linewidths are highly Doppler-broadened in dissociative excitation, and display two distinct kinetic energy distributions: which indicate that both purely repulsive and discrete, bound, excited molecular states, which then predissociate, are involved in the dissociation process that leads to the excitation of OI 7774 A. The magnitude of the measured cross-section and the fragment kinetic energy distribution both indicate that the previous time-of-flight studies of the metastable OI (5S0) state require reinterpretation.

Erdman, P. W.↗
NASA NTRS1987

A study of the infrared emission from the O I (3d 3D0) and (4s 5S0) states produced by electron impact excitation of O2

The absolute emission cross section values for the O I(3p 3P-3d 3D0, lambda = 11,287 A) and the (3p 5P-4s 5S0, lambda = 11,299 A) multiplets excited by electron impact on O2 have been measured. These infrared oxygen emission features appear prominently in auroral spectra and were observed in electron bombardment of O2. The former cross section has a value of 3.05 x 10 to the -19th + or - 15 percent at 100 eV, while the latter's value is 4.14 x 10 to the -19th sq cm + or - 15 percent. The quintet emission at lambda = 11,299 A is the only deexcitation channel for the 4s 5S0 state and thus represents the total excitation cross section for that state. However, the lambda = 11,287 A branch from the O I (3d 3D0) state only constitutes about 25 percent of the total 3d 3D0 cross section, with the major branch from this state being the transition to the ground state observed at lambda = 1027 A. The branching ratio is in good agreement with the theoretical calculation of Padhan and Saraph (1977).

Erdman, P. W.↗
NASA NTRS1987

Remote sensing of atomic oxygen - Some observational difficulties in the use of the forbidden O I 1173-A and O I 1641-A transitions

Recent sounding rocket and satellite studies suggest that simultaneous measurements of the O I 989-A and 1304-A resonance lines and of the forbidden 1172.6-A and 1641.3-A transitions would form the basis of a useful remote sensing technique for measuring the O I density and optical opacity of a planetary or stellar atmosphere. Because the 1172.6-A and 1641.3-A emissions are weak lines and are emitted in a wavelength region rich in spectral features, it is important to determine whether typical flight instruments can make measurements with sufficient spectral purity so that the remote sensing observations will yield accurate results. A detailed, high-resolution study of the far UV emission features in the regions surrounding the atomic oxygen transitions at 1172.6 and 1641.3 A was made. These spectra, which were excited by electron impact on O2 and N2, are presented in an attempt to display some potential sources of interference in aeronomical measurements of these O I lines. Both atomic and molecular emissions are found, and the spectral resolution necessary to make unambiguous measurements is discussed.

Erdman, P. W.↗
NASA NTRS1986

Electron impact excitation of the O I lambda 1172.6 A multiplet

The cross section for the dissociative excitation of the O I 1172.6 A multiplet is measured by the bombardment of O2 by 100 eV electrons. A cross section value of about 1.56 x 10 to the -22nd sq cm + or - 30 percent and an O I 1173 A/O I 989 A branching ratio of about 0.00013 + or - 35 percent are obtained. The branching ratio values are compared to the data of Morrison (1985) and Garstang (1961). The data reveal that the 1173 A branch from the O I (3s prime 3D0) state is not large enough to account for the discrepancy between the predicted and observed O I 989 A intensity in the earth's upper atmosphere.

Erdman, P. W.↗
NASA NTRS1986

Dissociative excitation of the N(+)(5S) state by electron impact on N2 - Excitation function and quenching

Metastable N(+)(5S) ions were produced in the laboratory by dissociative excitation of N2 with energetic electrons. The resulting radiative decay of the N(+)(5S) state was observed with sufficient resolution to completely resolve the doublet from the nearby N2 molecular radiation. The excitation function was measured from threshold to 500 eV. The cross section peaks at a high electron energy and also exhibits a high threshold energy both of which are typical of dissociative excitation-ionization processes. This finding complicates the explanation of electron impact on N2 as the mechanism for the source of the 2145 A 'auroral mystery feature' by further increasing the required peak cross section. It is suggested that the apparent N(+)(5S) quenching in auroras may be an artifact due to the softening of the electron energy spectrum in the auroral E region.

Erdman, P. W.↗
NASA NTRS1986

Electron-impact of the OI 1641.3 A line emission

The cross section for the dissociative excitation of the forbidden OI(2p41D-3s3S, 1641.3 A) transition by electron impact on O2 is measured. At 100 eV, a cross section value of 1.22 x 10 to the -23/sq cm + 2 - 35 percent is found. This result is consistent with recent estimates of this branching ratio from theoretical calculations and aeronomical observations and supports the suggestion by Meier et al. (1985) that observation of the OI 1641.3 A line would be useful for remote monitoring of atomic oxygen in the upper atmosphere.

Erdman, P. W.↗
NASA NTRS1985

Electron impact excitation of atomic oxygen - Revised cross sections

Revised cross-section values for the excitation of three O I resonance transitions at 1304, 1027, and 989 A, by electron impact on atomic oxygen are presented from threshold to 300 eV. These results are smaller than the excitation cross sections used in some airglow models by a factor of about 2.8. The revised values are in good agreement with recent quantum-scattering calculations. The downward revision is required by new laboratory studies in which the direct and dissociative cross sections for 1304 A excitation were normalized with small probable error to the O and O2 ionization cross sections. The results also reflect new advances in VUV optical calibration techniques. A number of outstanding airglow problems are simplified by these revisions.

Zipf, E. C.↗
NASA NTRS1983

Linewidth studies on the the NI(4S-4P) resonance multiplet

Doppler broadening of the 8691, 8212, and 1200-A multiplet lines of N I is investigated experimentally, and its implications for the interpretation of the earth's 1200-A UV dayglow are considered. A regulated 100-eV, 1-mA electron beam is passed through N2 at 300 K and about 0.0005 torr flowing through a collision chamber within a UHV system, and the radiation emitted is observed with a temperature-stabilized short-focal length monochromator with a bandpass of 0.2 A in the IR and an effective UV resolution (in second-order operation with a 3600-groove/mm plane grating) of about 0.04 A. Both the IR and VUV lines are found to be broadened to about 25 times the thermal Doppler linewidth, with the IR transitions accounting for more than half of the total N(4P) cross section at 100 eV. The kinetic energy of the N(4P) atoms produced by dissociative excitation is such that their 1200-A resonance radiation (2p2 3s4P - 2p3 4SO) would be optically thin in the upper atmosphere, contrary to what has been observed. A need to revise some aspects of current UV-dayglow models is identified.

Erdman, P. W.↗
NASA NTRS1983

Electron-impact excitation of the Cameron system (a(3)pi yields x(1) Sigma) transition of CO

The results of experimental observations of the Cameron bands of CO produced by electron impacts with CO and CO2 are presented, noting that the bands have been detected in the atmospheres of both Mars and Venus. The study was initiated to account for Conway's (1981) data that the Martian airglow displayed cross-sectional dissociative excitation of the Cameron bands seven time larger than laboratory measurements by Ajello (1971). Spectrometer measurements were obtained of processes occurring in a chamber filled with CO or CO2 gas being bombarded by an electron beam. A value three times higher than the previous lab oratory estimate was obtained. Reasons for the discrepancy are discussed, including a present factor of two error in laboratory estimates.

Erdman, P. W.↗
NASA NTRS1982

Closed-cycle cryogenic pump suitable for sounding rockets use

We have successfully used a closed-cycle cryogenic cooling system as a high-speed UHV pump for instruments carried into the upper atmosphere on board sounding rockets. The device utilizes a commercially available, Sterling-cycle refrigerator that has proven to be rugged and simple to use under field conditions.

Erdman, P. W.↗
NASA NTRS1980

A laboratory study of the lambda 2145 A auroral mystery feature

The prominent emission feature near 2145 A in the ultraviolet spectrum of an aurora has been tentatively identified by Dick (1978) as the doublet lines, 2139.68 A and 2143.55 A, emitted by metastable N+(5S) ions, and dissociative excitation of N2 by electron impact with a cross section greater than or equal to 2 x 10 to the -18th sq cm has been proposed as the source of this species. A detailed laboratory study of dissociative excitation is described that suggests two alternative viewpoints of this process: (1) If the calculated radiative lifetime for the N+(5S) state (4.4 microsec) is correct, then the N+(5S) dissociative excitation cross section is less than 3 x 10 to the -21st sq cm. Thus, a new N+(5S) source mechanism would have to be found in order to account for the auroral data. (2) If dissociative excitation does form N+(5S) ions efficiently, then the laboratory and field observations imply a radiative lifetime for this state of more than 10 msec, thus suggesting that there are major errors in the lifetime computation.

Erdman, P. W.↗