R. Claude Woods

A STUDY OF THE ACCURACY OF VARIOUS LANGMUIR PROBE THEORIES

Ion and electron densities have been measured in long, low pressure, cylindrical nitrogen and helium dc discharges using computer‐controlled Langmuir probes. Cylindrical probe data have been analyzed with a variety of theories in order to determine the latter’s accuracy. Electron densities were obtained from the electron saturation currents using orbital motion limited (OML) theories, and from the electron retardation region of the probe trace by integration of the second derivative of the probe current. Ion densities were obtained from both OML and radial motion analysis of the ion saturation currents. Line integrated microwave interferometry and discharge current continuity considerations in the positive column have been used to obtain two independent electron density measurements. While both probe electron density methods agree very well with each other and reasonably well with the independent density measurements, the OML theory applied to the ions overestimates the plasma density by up to a factor of...

Laser-induced fluorescence measurements of transverse ion temperature in an electron cyclotron resonance plasma

Laser‐induced fluorescence has been used to measure the Doppler profile of a transition in N+2 [the R18 component of the X2∑+g(ν = 0)⇒B2∑+u(ν = 0) band] in a pure N2 electron cyclotron resonance (ECR) plasma. The transverse ion temperature (Ti⊥) was determined from the measured width of the Doppler broadened transition. The measurements were made on axis, 41 cm downstream (‖B‖∼170 G) from the first electron cyclotron resonance. We found Ti⊥ decreased from 0.25 to 0.12 eV as the corresponding downstream neutral pressure increased from 0.5 to 4.0 mTorr. These results have important implications for the use of ECR devices for plasma etching, since Ti⊥ may determine the ultimate limit to the anisotropy of the etch.

The laboratory microwave spectrum of the cyanide radical in its X 2Σ+ ground state

The microwave absorption spectrum of the CN molecule in the v=0 and v=1 vibrational states of the electronic ground state has been obtained in glow discharges in nitrogen–cyanogen mixtures at room temperature. Zeeman modulation is used for detection of the signal, and the microwave source is phase locked and digitally programmed by a computer. For each vibrational state the frequencies of the seven strongest hyperfine components of the N=0→1 rotational transition have been extracted from a careful regression analysis of the complex line shapes observed in the digitized spectral data. For the v=0 state the resulting rest frequencies and molecular parameters are in good agreement with, but more precise and accurate than, the values obtained from earlier radioastronomical studies. For the excited vibrational state the present work provides the first determination of the hyperfine parameters. The precision of the results for both states is sufficient to give a reliable measure of the variation of the spin–rot...

Laboratory microwave spectrum and rest frequencies of the N/sub 2/H/sup +/ ion

The J = 1 reverse arrow 0 multiplet of N/sub 2/H/sup +/ has been detected in laboratory glow discharges in mixtures of hydrogen and nitrogen. This constitutes the first observation of this species in the laboratory by any spectroscopic method. A pattern of three lines, due to the quadrupole hyperfine splitting of the outer nitrogen, was observed, and the frequencies of these three lines were measured with the following results: F = 2 reverse arrow 1, ..nu.. = 93,173.70 +- 0.04 MHz, F = 1 reverse arrow 1, ..nu.. = 93,171.88 +- 0.04 MHz, and F = 0 reverse arrow 1, ..nu.. = 93,176.13 +- 0.22 MHz. These are in very good agreement with previous astronomical measurements.

An ab initio investigation of the spectroscopic properties of BCl, CS, CCl+, BF, CO, CF+, N2, CN−, and NO+

Spectroscopic properties have been calculated for the diatomics BCl, CS, CCl+, BF, CO, CF+, N2, CN−, and NO+ by Mo/ller–Plesset many‐body perturbation theory through MP4SDQ (fourth order with single, double, and quadruple substitutions). Very good agreement of both rotational and vibrational constant predictions with experiment was found at the MP4SDQ level of theory with the extended basis sets used (66 CGTO’s). CI dipole moments, which appear to be accurate to at least 0.1 D, and electric field gradients, which yield eq0Q values accurate to within 1–2 MHz, were obtained.

Theoretical molecular structures and electric dipole moments of CCCNH, HCCNC, HCCCNH+, NCNC, and NCCNH+

Molecular structures and energies have been computed at the double zeta SCF level for several linear triple bonded molecules that are either isomers or protonated forms of the familiar molecules cyanoacetylene and cyanogen. These structures have been used to predict rotational constants that can be used as a guide for locating or assigning laboratory or astrophysical microwave spectra. For the same molecules the dipole moments have been computed at the double zeta plus polarization configuration interaction level. Similar structure and dipole moment calculations have also been done on several related known molecules to assess the accuracy of the numerical results. All of the computed dipole moments fit into a pattern that can be roughly explained by simple polarization arguments.

Configuration interaction electric dipole moments for HCN, HNC, HNN+, HCO+ HBO, HBF+, and HCNH+☆

Abstract The SCF and CI dipole moments for HCN, HNC, HNN + , HCO + , HBO, HBF + , HCNH + are computed. The CI dipole moments for HCN and HNC are within 0.10 debye of their experimental values.

Complete active space self‐consistent field potential energy surfaces, dipole moment functions, and spectroscopic properties of O3, CF2, NO−2, and NF+2

Three‐dimensional potential energy and dipole moment surfaces have been calculated for the 24 electron triatomics O3, CF2, NO−2, and NF+2 using complete active space self‐consistent field wave functions (CASSCF) and a basis set of 87 (99 for NO−2) contracted Gaussian‐type orbitals (cGTOs). The analytical potential energy functions (PEFs) have been used in perturbation and variational calculations of anharmonic spectroscopic constants and vibrational energy levels. The results for O3 and CF2 are compared to the available experimental data, and predictions of the rotational and vibrational spectra of NO−2 and NF+2 have been made by comparison to these species. The equilibrium geometries of NO−2 and NF+2 are predicted to be re=1.260 A, θe=116.5° and re=1.242 A, θe=108.0°, respectively. The fundamental vibrational frequencies (ν1,ν2,ν3) and absolute band intensities (at 300 K) of these two ions are predicted to be 1286 cm−1/31 cm−2 atm−1, 782 cm−1/13 cm−2 atm−1, 1232 cm−1/2900 cm−2 atm−1 (NO−2) and 1272 cm−1/...

Laboratory detection of the 110←111 submillimeter wave transition of the H2D+ ion

The 110←111 transition of H2D+ was detected in a dc discharge in Ar–H2–D2 mixtures with liquid nitrogen cooling and an applied axial magnetic field. The transition frequency was determined to be 372 421.380±0.100 MHz. This transition is expected to be the most favorable one for radioastronomical detection of this very crucial ion in the interstellar medium.

The molecular structure of HCO+ by the microwave substitution method

Precise measurements of the frequencies of the J = 0–1 transition of HCO+, H13CO+, HC18O+, DCO+, D13CO+, and DC18O+ have been used to determine a substitution (rs) molecular structure for HCO+. The bond distances obtained are rs(CO) = 1.1071(2) A and rs(CH) = 1.0930(1) A. This is the first such microwave rs structure to be determined for any molecular ion. The determined bond distances and the transition frequencies can be compared to the results of previous high quality ab initio calculations and excellent agreement is found. An initial attempt to characterize the Doppler shifts of the HCO+ frequency due to ion drift in a dc discharge and a measurement of the J = 1→2 transition of DCO+, and thus its centrifugal distortion constant, are also reported here.