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We report a study of the complex AC impedance of chemical vapor deposition grown graphene. We measure the explicit frequency dependence of the complex impedance and conductance over the microwave and terahertz range of frequencies using our recently developed broadband microwave Corbino and time domain terahertz spectrometers (TDTS). We demonstrate how one may resolve a number of technical difficulties in measuring the intrinsic impedance of the graphene layer that this frequency range presents, such as distinguishing contributions to the impedance from the substrate. From our microwave measurements, the AC impedance has little dependance on temperature and frequency down to liquid helium temperatures. The small contribution to the imaginary impedance comes from either a remaining residual contribution from the substrate or a small deviation of the conductance from the Drude form. [ABSTRACT FROM AUTHOR]

In this paper a modification of the classical Weibull statistics is developed for nanoscale applications. It is called nanoscale Weibull statistics. A comparison between nanoscale and classical Weibull statistics applied to experimental results on fracture strength of carbon nanotubes clearly shows the effectiveness of the proposed modification. A Weibull’s modulus of ∼3 is deduced for nanotubes. The approach can treat (also) a small number of structural defects, as required for nearly defect-free structures (e.g., nanotubes) as well as a quantized crack propagation (e.g., as a consequence of the discrete nature of matter), allowing to remove the paradoxes caused by the presence of stress intensifications. [ABSTRACT FROM AUTHOR]

Many experiments on the mechanics of nanostructures require the creation of rigid clamps at specific locations. In this work, electron-beam-induced deposition (EBID) has been used to deposit carbon films that are similar to those that have recently been used for clamping nanostructures. The film deposition rate was accelerated by placing a paraffin source of hydrocarbon near the area where the EBID deposits were made. High-resolution transmission electron microscopy, electron-energy-loss spectroscopy, Raman spectroscopy, secondary-ion-mass spectrometry, and nanoindentation were used to characterize the chemical composition and the mechanics of the carbonaceous deposits. The typical EBID deposit was found to be hydrogenated amorphous carbon (a-C:H) having more sp2- than sp3-bonded carbon. Nanoindentation tests revealed a hardness of ∼4 GPa and an elastic modulus of 30–60 GPa, depending on the accelerating voltage. This reflects a relatively soft film, which is built out of precursor molecular ions impacting the growing surface layer with low energies. The use of such deposits as clamps for tensile tests of poly(acrylonitrile)-based carbon nanofibers loaded between opposing atomic force microscope cantilevers is presented as an example application [ABSTRACT FROM AUTHOR]

In this work, we have used the mechanical resonance method to determine the bending modulus of amorphous SiO[sub 2] nanowires and to study an electron charge trapping effect that occurs in these nanowires. For uniform amorphous nanowires having diameter ∼100 nm and length over 10 µm, the fit modulus values cluster near 47 GPa; this value is lower than the commonly accepted value of ∼72 GPa for fused silicon oxide (glass) fibers. For some SiO[sub 2] nanowires, we observed up to three closely spaced resonances that are a result of the nanowire anisotropy. We have compared the resonance vibration of nanowires driven by mechanical and also ac electrical field loading. All of the measurements were done inside the chamber of a scanning electron microscope where the nanowires were under bombardment of a flux of ∼3 keV energy electrons. By watching the interaction between the ac electrical field and exposed nanowire when driven at resonance frequency, we have observed significant charge trapping in the nanowires. The combination of charge trapping and decay time was nonuniformly distributed along the nanowire. This suggests a nondestructive method that can be used for studying defects in certain types of nanostructures. [ABSTRACT FROM AUTHOR]

Rotational spectra of several isotopic species of the SiF4–NH3 dimer were obtained with the Mark II Flygare–Balle FT-MW spectrometer. This is the first determination of the gas phase structure of a penta-coordinated silicon. The spectra indicate a symmetric top, trigonal bipyramid SiF3N structure with the lone electron pair of the NH3 pointed at one face of the SiF4 and the three equatorial F’s splayed significantly away from the N. The /_ Fax–Si–Feq is about 12° less than tetrahedral. The Si–N distance is determined to be 2.090 Å. The experimental results are in excellent agreement with the SiF4 deformation predicted by the ab initio calculations of Rossi and Jasinski [Chem. Phys. Lett. 169, 399 (1990)]. The measured dipole moment is 5.61 D, an enormous enhancement compared to the sum of the monomer moments, 1.47 D. The increase of 4.14 D is due largely to the geometric distortion of the tetrahedral SiF4 molecule upon dimer formation, demonstrating that the Si–F bond is much more ionic than covalent. If the charge is simply partitioned between Si and F so as to obtain a moment of 4.14 D, the Si has a charge of +3.52 and each F, -0.88. This conclusion is consistent with recent applications of the atoms-in-molecules charge partition methodology developed by Bader and co-workers. [ABSTRACT FROM AUTHOR]

A simple classical mutual polarization model accurately predicts the induced dipole moments of linear HCN dimer and trimer. The model employs the first four nonzero electrical molecular moments of each HCN, and both the molecular polarizability and the C–H and C–N bond dipole polarizabilities. The model is extended to linear H-bonded oligomers up to the pentamer, and also to an infinite linear H-bonded chain, appropriate for comparison with the H-bonded chains present in the HCN crystal. For the dimer and trimer, a relation is seen between the change in the electric field gradient at the N of HCN and the calculated induced C–N bond dipole moment. A semiquantitative proportionality constant, derived based on this relation, is used to enhance understanding of the underlying cause of the large increase in the 14N quadrupole coupling constant in the HCN crystal relative to the free HCN monomer. This increase results from the strong polarization of the C–N bond by the local field at each HCN caused by the rest of the HCN crystal lattice. [ABSTRACT FROM AUTHOR]

This work is the counterpart of a previous report on the (HCN)2–Y trimers with Y=HF, HCl, HCF3, and CO2 [J. Chem. Phys. 90, 4069 (1989)]. Rotational spectra have been observed for several isotopic species of the OC–, N2–, H3N–, and H2O–(HCN)2 trimers, using a pulsed nozzle, Fourier transform Balle/Flygare microwave spectrometer. The structures are basically composites of those reported for the (HCN)2 and X–HCN dimers. The trimers are effectively axially symmetric, but have some shrinkage of dimensions. Rotational constants found for the main isotopic species of each trimer are: For X=OC, a B0 of 421.142 MHz and DJ of 110 Hz; for X=N2, 435.573 MHz and 155 Hz; for X=H3N, a symmetric top, a B0 of 675.777 MHz, DJ of 180 Hz, and DJK of 41.1 kHz; and for X=H2O, with C2v symmetry, a (B0+C0)/2 of 667.028 MHz, (B0-C0)/2 of 0.617 MHz, DJ of 173 Hz, and a DJK of 62.9 kHz. The rotational constants for the isotopic species of each trimer were used to determine the distances r1 and r2 between the centers of mass (c.m.) of adjacent monomers, r1 being that for X–HCN and r2 that for (HCN)2. For X=OC, N2, H3N, and H2O the shrinkages found in r1 are 0.068, 0.056, 0.084, and 0.074 Å, respectively, and in r2 0.013, 0.013, 0.044, and 0.026 Å. The 14N quadrupole coupling constants were determined by selective 15N substitution for most of the nitrogen sites in the trimers. The effects of charge redistribution in the trimers were separated from those of torsional oscillations in several instances including N2 in N2–(HCN)2. [ABSTRACT FROM AUTHOR]

We have studied the relaxation of conformers and the formation/relaxation of isomeric, weakly bonded dimers in pulsed supersonic expansions of seeded inert gases (He, Ne, Ar, Kr). The relaxation was determined from the intensity of a rotational transition for the higher energy species as a function of carrier gas composition, using the Balle/Flygare Fourier transform microwave spectrometer. Of thirteen molecules with rotational conformers which we examined, those with barriers to internal rotation greater than 400 cm-1 did not relax significantly in any of the carriers. The higher energy forms of ethyl formate, ethanol, and isopropanol, with smaller barriers, were not relaxed by He; those of ethanol and isopropanol were somewhat relaxed by Ne; and all were completely relaxed by as little as 5 to 20 mole percent of Ar or Kr in He or Ne. The relaxation in He or Ne is first order in the concentration of added Ne, Ar, or Kr as well as in the concentration of the high energy conformer. The pseudo first-order rate constants (larger in Ne than in He) increase sharply with Z of the rare gas, roughly in a 0:1:2:4 progression for He, Ne, Ar, and Kr, suggesting that the relaxation involves relatively long-range polarization effects. Similar behavior was found in the formation/relaxation of the weakly bonded dimer pairs: linear OCO–HCN, T-shaped HCN–CO2; linear FH–NNO and bent NNO–HF; and bent HF–DF and DF–HF. The case of the HCN/CO2 dimers is particularly striking. The T-shaped dimer was found first, using Ar as the carrier gas. Five years later the linear form was found with first run neon as carrier, but it could not be detected at all with Ar as the carrier. These results show that in favorable cases high energy species can be studied in supersonic expansions by freezing out a ‘‘high-temperature’’ concentration with a nonrelaxing carrier gas. [ABSTRACT FROM AUTHOR]

Microwave rotational spectra have been observed for a number of isotopic species of the (HCN)2–HF, –HCl, –HCF3, and –CO2 trimers. The observations were made with the pulsed nozzle, Fourier transform, Flygare/Balle Mark II spectrometer. The trimers have structures which are composites of the linear (HCN)2 dimer and the HCN–Y dimers, the latter linear for Y=HF and HCl, a symmetric top for Y=HCF3, and T-shaped with C2v symmetry for Y=CO2. The rotational constants for the most abundant species of each trimer are as follows: For Y=HF and HCl, B0 is 699.204 and 467.408 MHz, respectively, and DJ is 162 and 87 Hz; for Y=HCF3, B0 is 305.742 MHz and DJ and DJK are 51 and 471 Hz; for Y=CO2, treated as a symmetric top, (B0+C0)/2 is 452.426 MHz and DJ is 1.057 kHz. Hyperfine interaction constants were determined for several species. The B0’s for each trimer were analyzed by a combination of isotopic substitution and fitting procedures to determine the distances r1 and r2 between the centers of mass (c.m.) of adjacent monomers. The B0’s are relatively insensitive to the position of the central HCN but give r1+r2 accurately. With this limitation, r1 and r2 in the trimers are compared with the corresponding distances in the dimers, which are longer. For Y=HF, HCl, HCF3, and CO2, respectively, the shrinkages found in r1 are 0.069, 0.054, 0.030, and 0.004 Å and in r2, 0.043, 0.062, 0.042, and 0.052 Å. The shrinkage in r1 and several other properties of the trimers exhibit some correlation with the pseudodiatomic stretching force constant in the HCN–Y dimer. [ABSTRACT FROM AUTHOR]

A linear hydrogen-bonded dimer, OCO–HCN, has been identified and characterized via its microwave rotational spectrum. The study was made using the pulsed nozzle Fourier transform method with the Flygare/Balle Mark II spectrometer. A T-shaped HCN–CO2 dimer was reported earlier by the Klemperer group. Rotational constants have been determined for all seven monoisotopically substituted species of the linear form. B0 , DJ , and χaa (14 N) for the normal isotopic dimer are 1057.9397(2) MHz, 1.372(8) kHz, and -4.2466(5) MHz, respectively. The average torsional displacements of the OCO and HCN monomers about their center of mass (c.m.) are found to be 7.66° and 12.40°, based on the substitution O–C and C–N bond distances for the dimer. With these values for α and γ, the B0 for the normal isotopic dimer corresponds to a c.m. to c.m. distance R=5.035 Å. Bending and stretching force constants and the well depth (ε∼590 cm-1 ) are estimated from the centrifugal distortion. The relative concentrations of the linear and T-shaped isomers are unusually sensitive to the carrier gas used in the supersonic jet expansion. The linear form could not be detected at all with argon as the carrier gas but gave a strong signal in neon first run (70% Ne, 30% He). In contrast, the T form gave strong signals in both carrier gases. However, a carrier-gas effect was not found for the N2 O/HF dimer pair, which has a high barrier between the bent NNO–HF and linear FH–NNO isomers. Similar results were obtained for chlorocyclohexane (CCH) and ethyl formate (EF), which have two conformational isomers. In CCH which has a high barrier to a↔e interconversion, the two conformers gave strong signals in both Ar and He. In EF, with a low barrier, the gauche conformer could not be detected in Ar but gave a strong signal in He, while the trans form gave strong signals in both carrier gases. [ABSTRACT FROM AUTHOR]

Microwave rotational spectra have been observed for 22 isotopic species of an HCN, hydrogen-bonded trimer with the pulsed nozzle, Fourier transform method using the Flygare/Balle Mark II spectrometer. The 14N nuclear quadrupole hyperfine structure was analyzed and the interaction constants and line centers determined. The line centers were fitted to obtain ground vibronic state rotational constants. For the normal isotopic species of (HCN)3, B0 was found to be 469.3073(1) MHz and DJ, 82.6(1) Hz. The quadrupole coupling constants χ(n) are -4.049(2), -4.251(2), and -4.375(1)MHz for n=1, 2, and 3, respectively, in HCN(1)HCN(2)HCN(3). The trimer has a linear or very near linear equilibrium structure. The B0’s are insensitive to the position and torsional oscillations of the central HCN but they determine the outer HCNs quite accurately. An isotopic substitution method gives R, the c.m. distance between the outer HCN’s, to be 8.790 Å in the 14–14–14 species. A slightly smaller value 8.788 Å is obtained from a fit of the B0’s which includes the effects of isotopic substitution on the H/D–C and C–N bond lengths in the monomer. The distance between c.m.(1) and c.m.(2) may be somewhat shorter (∼0.01 Å) than that between c.m.(2) and c.m.(3). The average c.m. separation in the trimer (4.395 Å) is halfway between that of the dimer (4.447 Å) which is known to be linear and the infinite linear chains in the solid (4.34 Å). It is shown that the smaller quadrupole coupling constants in the trimer compared to the monomer are caused by a combination of torsional and charge redistribution effects. The torsional vibrations have average angular displacements of 12.60° and 8.55° for HCN(1) and HCN(3). The charge redistribution effect upon χ in the trimer (6.5%) is about 1.8 times that in the HCN dimer. The dipole moment of the trimer was found to be 10.6 D, a value enhanced by 1... [ABSTRACT FROM AUTHOR]

Microwave rotational spectra have been observed for the four 14N/15N isotopic species of an (HCN)2–Ar trimer with the pulsed nozzle Fourier transform method using the Flygare Mark II spectrometer. Thirteen J→J’ asymmetric top transitions were measured in the 2.5 to 10 GHz region for the parent 14N,14N trimer and nine for each of the other three species. The 14N nuclear quadrupole hyperfine structure was analyzed for the transitions and the interaction constants and line centers determined. The line centers were fitted to obtain ground vibronic state rotational and quartic centrifugal distortion constants. For the 14N/14N trimer these are (in MHz) for A‘, B‘, and C‘: 2013.5993(10), 1759.2756(3), 932.3709(2); and for τ1, τ2, τaaaa, τbbbb, and τcccc[ATOTHER]@B:[/ATOTHER]-0.3017(1), -0.0660(1), -0.1700(9), -0.013 71(1), and -0.0088(1). The inertial defect is 3.7881 amu Å2. The zero-point vibrationally averaged geometry is planar and T shaped with the structure of the linear HCN dimer remarkably unperturbed by presence of the Ar atom. The substitution N···N distance in the cluster is 4.453 Å compared with 4.461 Å in the free dimer. The argon is attracted by the π electrons of the two –C≡N groups, being equidistant from them. The Ar···N(1) and Ar···N(2) distances are 3.671 and 4.316 Å, respectively. [ABSTRACT FROM AUTHOR]

The Ar3–HCl tetramer has been identified via the observation of its microwave rotational spectrum using the pulsed nozzle Fourier transform technique. The rotational spectroscopic constants of the ground vibrational state have been obtained for the 35Cl/37Cl isotopes from measurements of the J=1→2 to J=4→5 transitions and their hyperfine structure. For Ar3–H35Cl, the values found for B0, DJ, DJK, and χaa are 843.8974(1) MHz, 2.333(2) and 1.818(6) kHz, and 31.006(5) MHz, respectively, and for Ar3–H37Cl, 825.9811(2) MHz, 2.211(5) and 1.940(12) kHz, and 24.481(8) MHz. The cluster is a symmetric top with the HCl along the C3 axis, its H end directed towards the Ar3 trimer. In its torsional oscillations, the HCl makes an average angle of 36.91° with the symmetry axis. The chlorine isotopic substitution leads to values of 3.8510 and 4.0024 Å for the Ar–Ar and Ar–Cl distances. The results of the present study are compared with those reported earlier for the Arm–HF (m=1,2,3) and Arm–HCl (m=1,2) clusters. [ABSTRACT FROM AUTHOR]

Rotational spectra have been observed for eight isotopic species of the diborane–HCl complex with a Balle–Flygare, pulsed nozzle, Fourier transform microwave spectrometer. The dimer has a linear, or at most slightly bent B–B···H/DCl equilibrium structure with the H/D end of the HCl attracted symmetrically to a terminal BH2 group of the diborane. Three B2H6–HCl species homonuclear in the boron were observed to tunnel while those with 10B11BH6 or DCl did not. The tunneling splits each rotational transition into two components of comparable intensity, separated by several MHz depending on J and K. The a–dipole transitions are characteristic of a prolate, very near symmetric top; only K=0 and ±1 transitions were found. Rotational constants are reported for all species. The B, DJ, H, (B-C), and DJK constants determined for 11B2H6–H35Cl are for the A1 tunneling state 1273.364(1) MHz, 5.56(5) kHz, 1.0(8) Hz, 5.3(2) MHz, and -2.1(3) MHz; for the A2 tunneling state 1273.856(1) MHz, 11.64(7) kHz, 33.1(9) Hz, 5.70(4) MHz, and -3.21(5) MHz. The chlorine hyperfine structure gives the average torsional displacement of the H/DCl from the a axis to be 26.3° for the HCl complexes and 22.5° for the DCl. The torsional displacement of the B2H6 was found by an inertial analysis of the complexes with HCl. It is very anisotropic, being close to 0° in the ethylene plane and about 9° in the BH2B bridging plane. It is suggested that in the tunneling the B2H6 reorients by 180° in the bridging plane, coupled with a gear-like counter rotation of the HCl by 360°. The B···H distance is 2.693 Å in the dimers with HCl and the B···D distance is slightly longer, 2.702 Å. [ABSTRACT FROM AUTHOR]

Rotational spectra are reported for several isotopic species of the OC–and H3N–HCN–HF heterotrimers, detected with a pulsed nozzle, Fourier transform, Balle/Flygare microwave spectrometer. Rotational constants for the main isotopic species of the OC trimer are a B0 of 615.574 MHz and DJ of 251 Hz, and for H3N, a symmetric top, a B0 of 1067.161 MHz and DJ and DJK of 0.40 and 63 kHz. Their structures are composites of those reported for the X–HCN and HCN–HF dimers. They are effectively axially symmetric but have some shrinkage from the distances in the dimers. The shrinkages found in r1, the c.m. to c.m. distance for X–HCN are 0.070 and 0.098 Å for X=OC and H3N, respectively, and in r2 for HCN–HF, 0.033 and 0.027 Å. The 14N and H–F hyperfine interactions in OC–HCN–HF are the same as those reported for the HCN–HF dimer. Detection of the X=OC and H3N trimers out of the many species possible required care in their generation. Both were favored by the strongly bonded HCN–HF subunit. The OC–HCN–HF was further enhanced by using a high concentration of CO in the gas expansion. For H3N–HCN–HF a coaxial mixing nozzle was developed to avoid the formation of NH4F(s). The selectivity and simplicity of the nozzle should be helpful in extending the range of species observable with pulsed nozzles. [ABSTRACT FROM AUTHOR]

Microwave rotational transitions have been observed for HCN–(CO2)3, DCN–(CO2)3, H13CN–(CO2)3, HC15N–(CO2)3, HCN–(13CO2)3, HCN–(18OCO)(CO2)2, and HCN–(CO2)(C18O2)2 with the pulsed Fourier transform, Flygare/Balle Mark II spectrometer. A symmetric top spectrum was observed for the parent isotopic species with rotational constants of B0=861.6392(1) MHz, DJ =0.681(5) kHz, and DJK =0.821(12) kHz. The results for isotopic substitution indicate a zero-point, vibrationally averaged geometry having the C3 symmetry of a cyclic (CO2)3 structure with the HCN along the symmetry axis and the N end closest to the (CO2)3. The C3 symmetry is confirmed by the observation of states limited to K=±3n, with n=0,1,2,..., as predicted for threefold symmetry generated by bosons only. The (CO2)3 has a pinwheel configuration, as in the free trimer, and the three carbons lie in a plane R=2.758 Å below the center of mass (c.m.) of the HCN. The C-C distance in this subunit is 3.797 Å which is 0.241 Å shorter than that found in the free (CO2)3 trimer. The individual CO2’s in the (CO2)3 pinwheel are rotated out of the C–C–C plane by γ=-6.9°, as determined from an inertial analysis, with the inner oxygens rotated away from the HCN. The HCN has an average torsional angle of 10.3°, as determined by isotopic substitution, and an observed χcc value of -3.891 MHz for the 14 N. The c.m.(HCN) to C distance is 3.525 Å, compared to 3.592 Å in the HCN-CO2 T-shaped dimer. The isotopic substitution by 18O perturbs the structure of the symmetric top clusters by a remarkable amount, decreasing γ to -28.9° and increasing R and RCC to 2.797 and 3.814 Å, respectively. In the 18O substituted species, the CO2’s are rotated in the C–C–C plane from C3v symmetry by the pinwheel angle β=∼32.5°. [ABSTRACT FROM AUTHOR]

We have studied rovibrational state mixing in acetaldehyde using infrared laser induced fluorescence. Molecules are isolated and cooled in supersonic molecular beams, and irradiated in the C–H stretch fundamental region with an infrared optical parametric oscillator. Spectral resolution is provided with either a circular variable filter machine or a cryogenic Michelson interferometer. We have found evidence of several strong Fermi resonances between the aldehyde C–H stretch and a few overtones and combinations of lower frequency modes. In addition, there is substantial random state mixing in this region as evidenced by the average experimental dilution factor of 0.2. The dependence of the dilution factor on the average J excited by the laser shows that the extent of state mixing scales linearly with J. We have observed from dispersed fluorescence spectra that random rotational coupling occurs between different Kp states. Our previous statistical coupling model has been applied to the interpretation of the data, and its applicability is discussed. For the model calculation, the methyl torsion is specially treated as a very anharmonic mode in the eumeration of the zeroth order bath states. The average coupling width derived from the model calculation is 0.35 cm-1. The relative energy content apportioned among vibrational modes in the molecule following excitation is measured and is successfully explained with the model. [ABSTRACT FROM AUTHOR]

The 40Ar4–HF and –DF clusters have been identified and characterized by their microwave rotational spectra using a Flygare–Balle FT spectrometer with a pulsed supersonic nozzle to generate and detect the clusters. The observed J=2→3 to 6→7 transitions have fine structure limited to K=0, ±3 and ±6, indicative of symmetric tops with a threefold axis of symmetry produced by I=0 nuclei. For Ar4–HF the rotational constants B0, DJ, and DJK are 623.4539(1) MHz, 1.062(1) kHz, and 0.611(31) kHz, respectively; and for Ar4–DF, 618.5846(1) MHz, 1.030(1) kHz, and 0.665(4) kHz. The results show that the clusters consist of the trigonal Ar3–H/DF tetramer reported earlier, with a fourth argon on the back side of the Ar3 group to form a tetrahedral or near tetrahedral Ar4. In both clusters the H/DF lies along the threefold axis of the Ar3 group, with the H/D end pointed at its face. If one assumes an Ar–Ar distance of 3.85 Å for both clusters, the Ar3 plane to HF c.m. distance for Ar4–HF with a tetrahedral Ar4 is 2.713 Å compared to 2.735 Å for Ar3–HF. The nuclear hyperfine structure of the rotational transitions shows that the H/DF experiences large amplitude bending vibrations with respect to the C3 symmetry axis. The average amplitude for HF (40.4°) is comparable with that reported for the smaller Arm–HF complexes (m=1, 2, 3). However, for DF the apparent 25.1 (1.6)° amplitude found is 10° less than that in the smaller complexes. The difference is attributed to an increased electric field gradient at the D in the pentamer. A possibly related feature is an Ar4 c.m. to F distance which is 0.013 Å longer for Ar4–DF than for Ar4–HF. [ABSTRACT FROM AUTHOR]

Microwave rotational spectra have been observed for both Cl isotopes of the Ar2–HCl trimer with the pulsed nozzle Fourier transform method using the Flygare Mark II spectrometer. The Cl nuclear quadrupole hyperfine structure was analyzed for each of the transitions and the coupling constants and line centers determined. Sixteen transitions were observed in the 2 to 15 GHz region for the 35Cl species and 11 for 37Cl. The line centers were fitted to obtain ground state rotational and quartic centrifugal distortion constants A‘, B‘, C‘, τ1, τ2, τaaaa, τbbbb, and τcccc. For Ar2–H35Cl, the values are 1733.857, 1667.932, 844.491, -0.1170, -0.0292, -0.1199, -0.0802, and -0.0079 MHz, respectively, and for Ar2–H37Cl: 1733.824, 1606.877, 828.497, -0.1121, -0.0279, -0.1205, -0.0737, and -0.0075 MHz. The equilibrium geometry is determined to be T shaped with C2v symmetry and the H end of the HCl closest to the Ar2. Large amplitude slightly anisotropic torsional motion of the HCl is evident from the hyperfine constants. The chlorine isotopic substitution enables the torsional displacement of the Ar2 dimer to be estimated. It is found to be an average of 7.3° with respect to the b axis. With allowance for the torsional effects, a value of 3.861 Å is obtained for the Ar–Ar distance and 4.005 Å for the Ar to Cl distance. An approximate, harmonic force field analysis is based on the centrifugal distortion constants. A comparison is given of the force constants and Ar–Ar distances for the Ar2–HCl and Ar2–H/DF trimers. [ABSTRACT FROM AUTHOR]

Silicon carbide films were grown on (100) silicon substrates by deposition of 200-nm-thick C[sub 60] films, followed by annealing. The predeposited C[sub 60] is progressively destroyed by annealing, and carbon reacts with silicon to produce SiC. The reaction starts at the interface and continues by diffusion of silicon through the already formed SiC. At the lower temperatures (700 °C), the reaction is localized at the interface. Diffusion of silicon and formation of stoichiometric SiC requires annealing at 800 °C for t ≥ 100 min and at 900 deg;C for t ≥ 25 min. The stoichiometric films are uniform with a grain size of 20-40 nm. A diffusion coefficient of silicon in SiC of 4 × 10[sub -15] cm²/s at 900 °C was determined. Because the diffusion of silicon is faster through preferential paths in the SiC film, such as grain boundaries and other crystalline defects, pits and voids are produced in the silicon substrate when the C[sub 60] predeposited film covers larger areas. [ABSTRACT FROM AUTHOR]