Microwave Absorption Spectra Research Articles

Soliton oscillations in DNA.

Longitudinal-acoustic-wave oscillations on circular and linear segments of DNA are analyzed for a Boussinesq model which includes both the effects of dispersion and of anharmonicity. Expressions are obtained for the frequency spectra of anharmonic (soliton) modes. These results may help to explain details of the microwave absorption spectra of DNA.

Cell membrane as a possible site of Fröhlich's coherent oscillations

The microwave absorption spectra of erythrocytes and their ghosts have a resonant structure and reveal a close resemblance, indicating that the cell membrane is the primary site of Fröhlich's coherent oscillations.

Selective excitation of magnetostatic modes of a thin film

A ferromagnetic resonance technique for selective excitation of various series of magnetostatic modes of a thin film is presented. Microwave absorption spectra of a YIG film are recorded in various configurations. The observed resonance fields for both surface and volume modes are found to be in good agreement with the fields calculated from a generalized form of the Damon-Eshbach formula.

The microwave spectrum of the PF radical in the ground X 3Σ− electronic state

The microwave absorption spectrum of the PF radical in the X 3Σ− state was detected by using a source modulation microwave spectrometer. The radical was produced in a free space cell by a dc glow discharge in a mixture of PH3 and CF4. Five rotational transitions with N=1 ← 0 up to 5 ← 4 were observed in the frequency region of 44 to 171 GHz and were least-squares analyzed to determine the rotational constant, the centrifugal distortion constant, the spin–spin coupling constant with its centrifugal distortion term, the spin-rotation coupling constant, and the magnetic hyperfine coupling constants for both phosphorus and fluorine nuclei. A centrifugal correction term was found to be necessary for the c magnetic hyperfine constant of phosphorus in order to achieve a good fitting of the observed spectrum. The present data agree with, but considerably improve the accuracies of ground-state molecular constants which Douglas and Frackowiak derived from high-resolution emission spectra. The spin density and the s character of the unpaired-electron orbital were calculated from the observed magnetic hyperfine coupling constants to be 91.3% and 0.88% for P and 9.1% and 0.17% for F.

The microwave spectrum of the SiN(2Σ+) radical

The microwave absorption spectrum of the SiN radical has been detected in a dc glow discharge in a SiCl4 or SiH4/N2 mixture. The three rotational transitions N=2←1, 3←2, and 4←3, have been observed in the frequency region 87 to 175 GHz by using a source-frequency modulation microwave spectrometer. The rotational constant, the centrifugal distortion constant, the spin-rotation coupling constant, and the magnetic hyperfine coupling constants b and c and the electric quadrupole coupling constant of the nitrogen nucleus have been precisely determined. The electronic structure of the SiN molecule has been briefly discussed using the magnetic hyperfine coupling constants and also the quadrupole coupling constant [3.05(23) MHz] of 14N.

Studies of microwave absorption in liquids by optical heterodyne detection of thermally induced refractive index fluctuations

A new method for obtaining the microwave absorption spectrum of optically transparent condensed media is described. Phase fluctuations impressed on a single‐frequency laser beam passing through a sample are detected by optical heterodyning. These phase fluctuations result from density fluctuations induced by the absorption of microwave energy. Preliminary experiments on water and ethanediol yield absorption spectra which are consistent with those obtained in previous investigations using conventional techniques.

ChemInform Abstract: THE STRUCTURE OF NITROSOACETYLENE BY AB INITIO METHODS

Abstract The geometrical structure of HCCNO has been calculated using ab initio SCF and GVB methods. Since it has not yet been prepared, attempts are made to predict spectroscopic constants related to its microwave, infrared and visible absorption spectra.

The structure of nitrosoacetylene by ab initio methods

The geometrical structure of HCCNO has been calculated using ab initio SCF and GVB methods. Since it has not yet been prepared, attempts are made to predict spectroscopic constants related to its microwave, infrared and visible absorption spectra.

Assignment of laser lines in an optically pumped submillimeter and near millimeter laser: (H2CO)3

A large number of emissions is obtained in the submillimeter and near millimeter range with the (H2CO)3 laser optically pumped by a CO2 laser. A study of the microwave absorption spectrum of the molecule carried out simultaneously with the submm analysis allows us to assign six of the laser lines in thev5 excited state of the molecule and to determine the rotational constants and vibrational energy ofv5.

Observation of new lines in the microwave spectrum of ortho-H2 pairs in solid hydrogen

New microwave absorption spectra of ortho pairs in low ortho concentration samples of solid hydrogen are reported. Three excited state transitions which fix the position of the 10 Γ level for both types of nearest neighbour pairs are reported, and compared with the theoretical predictions of Harris, Berlinsky, and Hardy and Luryi and Van Kranendonk. Several new lines from the out-of-plane configuration are reported which confirm previous assignments. In contrast, two new lines from the next nearest neighbour spectrum support a reassignment of transitions for this configuration. A fit to this data determines several of the anisotropic potential parameters for next nearest neighbours. The improvements in the microwave spectrometer essential to obtaining the new results are also described. Finally, we compare our results to the most recent theoretical potential parameters of Schaefer and Meyer. A long standing discrepancy between theoretical and experimental values for the phonon renormalizationof Γ appears to be resolved by use of the new potential which has a substantial (~10%) non-quadrupolar contribution to ε4(R).

The microwave spectrum of the OH X2Π radical in the ground and vibrationally-excited (ν ≤ 6) levels

The microwave absorption spectrum of the OH X2Π radical has been observed in all vibrational levels up to ν = 6. Experimental details are described of the tunable cavity and parallel plate Stark-modulated spectrometers employed for transitions below and above 23 GHz, respectively. The observed line frequencies, together with those reported by other workers, have been fitted using a non-linear least-squares routine with numerical diagonalization of the Hamiltonian matrix. Pseudo high-order corrections for centrifugal distortion of the Λ-doubling are required for the ν = 0 data, which now extend to J = 19/2 in the 2Π1/2 component. The various adjustable parameters of the Hamiltonian are compared with those of other similar models. The Λ-doubling and magnetic hyperfine constants for the different vibrational levels are reported, and several line frequencies of potential astrophysical significance are predicted.

Microwave magnetic resonance in amorphous GdAl films

The microwave absorption spectrum of amorphous sputtered ${\mathrm{Gd}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}$ films at 9.13 GHz exhibits a single broad line which is studied as a function of temperature and composition $x$. In the paramagnetic regime, the $g$ factor has a composition-independent positive shift of 0.006\ifmmode\pm\else\textpm\fi{}0.004 above 1.992 of the free ${\mathrm{Gd}}^{3+}$ ion, in contrast to negative shifts previously reported for crystalline GdAl. The shift is interpreted as arising from an exchange interaction ${J}_{\mathrm{df}}$ of the Gd $f$ shell with electrons of $d$ character. The $g$-shift contribution of the exchange interaction ${J}_{\mathrm{sf}}$ with $s$ electrons is presumed to be hidden because of a thermal bottleneck. This latter exchange interaction has a minimum value of 0.1 eV, as deduced from paramagnetic Curie temperatures. Using the observed temperature dependence of the resonance linewidth plus approximate band parameters from analogous dilute crystalline systems, the spin-lattice relaxation rate of amorphous ${\mathrm{Gd}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}$ is estimated to be ${10}^{13}x$ Hz, in order-of-magnitude agreement with dilute crystalline systems. At lower temperature the field for resonance shifts down, strongly for $x=0.37$ but less strongly for higher Gd concentration. This shift is interpreted as an effective anisotropy field arising from local demagnetizing fields of an inhomogeneous (spin-glass) system. The composition dependence of the shift indicates that with increasing Gd concentration, the alloy becomes more magnetically homogeneous, gradually approaching simple ferromagnetism.

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–rotation constant (γ) and the hyperfine constants (b, c, and eQq) with vibrational quantum number.

Comments on the microwave absorption spectrum of solid H 2

Recent theories by Luryi et al. and by Harris et al. for the energy levels of an isolated pair of ortho-H 2 molecules in nearly pure solid para hydrogen are compared.

Reduction of the Baseline Ripple on Spectra Recorded with the Parkes Radio Telescope

One of the factors determining system sensitivity in radio astronomy measurements of microwave emission and absorption spectra is the flatness of the spectrometer response in the absence of any spectral features. Ripple appears as a quasi-sinusoidal variation of this baseline and occurs whenever two or more components of the same signal reach the receiver by different paths and interfere.

Microwave absorption by ortho-H2 pairs in solid hydrogen

Measurements of the microwave absorption spectrum of pairs of (J = 1) H2 molecules at low concentration in (J = 0) solid hydrogen in the frequency ranges 10–26 and 60–90 GHz are reported. Observation of absorptions with coefficients 10−5 cm−1 is accomplished by a novel calorimetric method. These absorptions result from transitions between energy levels of near neighboring pairs of (J = 1) molecules and assignments are made on the basis of selection rules, relative intensities, temperature dependences, and time evolution due to migration of (J = 1) molecules. Clustering of in-plane and of out-of-plane nearest neighbor pairs are observed to have time constants of 100 and 10 h, at 1.2 K and with 0.2% concentration of (J = 1) species. Peak frequencies, widths, and line shapes are determined with a resolution typically of order 5 to 50 MHz. Comparison is made to theoretical expressions for the transition frequencies, developed in the following paper, and several anisotropic potential parameters are determined, namely: the effective quadrupole coupling constant [Formula: see text], non-quadrupolar coupling constants ε0 = −1.55 × 10−2 cm−1 and ε2 = 1.1 × 10−2 cm−1, the crystal field Vc = 9.8 × 10−3 cm−1, and the difference in the quadrupole coupling for in- and out-of-plane nearest neighbor pairs ΔΓ/Γ = −1.4 × 10−3. The intensities of the observed transitions agree reasonably well with those calculated assuming a quadrupole-induced-dipole absorption process and using known values of the polarizability tensor of the H2 molecule. At low (J = 1) concentrations, the line widths are generally caused by inhomogeneous variations in Γ. At higher concentrations, the line widths agree qualitatively with the theory of Fujio, Hama, and Nakamura for spectral width due to longer range quadrupole interactions, although the line shapes do not correspond very well. Tentative assignments of transitions from further than nearest neighbor pairs are proposed.

Infrared and microwave high-resolution spectrum of the ν 3 band of ozone

The vibration-rotation band ν 3 of ozone has been recorded with a high-resolution (0.012 cm −1) spectrometer, and microwave absorption spectra of ozone have been identified in the excited vibrational states (100) and (001). A strong Coriolis interaction has been observed. More than 1200 spectral lines have been identified in the ν 3 band, using a Watson-type Hamiltonian, including all the sextic centrifugal distortion terms. Band constants and an atlas listing line wavenumbers, intensities, and assignments are given, from 1007 to 1072 cm −1. It is shown that transitions with high values of the quantum numbers K −1 (≥11) contribute to significant absorption.

Formation, microwave spectrum and molecular constants of bismuth monochloride

The microwave absorption spectrum of gaseous bismuth monochloride (BiCl) in the O + electronic ground state has been measured in the 55–100 GHz region. The molecule was produced by a double oven technique at 500°C. Rotational transitions (ν, J +1) ??? (ν, J) with J = 10, 12, 16 and 17 and ν up to 9 were observed for Bi 35Cl and with J = 10, 12, 17 and 18 and ν up to 5 for Bi 37Cl. The hyperfine structure due to the Bi and Cl nuclei is generally only partially resolved. Analysis yields the following rotational and hyperfine constants for Bi 35Cl: Y O1 = 2761.8538(13) MHz, Y 11 = −12.0526(11) MHz, Y 21 = 11.62(32) kHz, Y 31 = 43(25) Hz, Y 02 = −987.2(22) Hz, eq 0 Q(Bi) = −1027(12) MHz, eq 0 Q ( 35Cl) = −34.5(28) MHz, c Bi = −21(7) kHz. The results for Bi 37Cl are: Y 01 = 2634.0416(18) MHz, Y 11 = −11.2268(10) MHz, Y 21 = 10.95(20) KHz, Y 02 = −896.8(31) Hz, eq 0 Q (Bi) = −1025(28) MHz, eq Q ( 37Cl) = −27.1(38) MHz, c Bi = 18(22) kHz. From Dunham coefficients we deduce potential and vibrational constants and from hyperfine constants some information about chemical bonding in BiCl. The results are in agreement with the position of Bi in the periodic system which is intermediate between the elements of group III a and VII a.

Rotational spectrum of BiBr

The microwave absorption spectra of Bi 79Br and Bi 81Br have been measured in the 65–100 GHz region. Frequencies of rotational transitions (υ, J + 1) ← (υ, J) in the 0 + electronic ground state with J = 26,27 and 35–39, and in the vibrational state υ = 0–11 can be fitted to the expression: ν = 2[ Y 01 + Y 11(υ + 1 2 ) + Y 21(υ + 1 2 ) 2] ( J + 1) + 4 Y 02( J + 1) 3. The results for the Dunham coefficients are: Y 01 = 1295.5609(12) MHz, Y 11 = −3.97809(18) MHz, Y 21 = 2.303(18) kHz, Y 02 = −220.26(45) Hz for Bi 79Br, and: Y 01 = 1272.3406(12) MHz, Y 11 = −3.87164(16) MHz, Y 21 = 2.225(14) kHz, Y 02 = −212.31(45) Hz for Bi 81Br. From these results we have deduced the value for the equilibrium distance r e, for the potential constants a 0 and a 1, and for the vibrational constants ω e and ω eχ e. The molecular constants of BiBr are almost the same as of TIBr, the situation found also for BiI and TII.

Collision-induced light scattering by compressed CF4and CF4-He mixtures

We have observed the collision-induced scattering from compressed C${\mathrm{F}}_{4}$ up to 70 atm and from C${\mathrm{F}}_{4}$-He mixtures at concentrations of 27%, 47%, and 48% C${\mathrm{F}}_{4}$, up to a total pressure of 155 atm. To describe the intensity distribution for pure C${\mathrm{F}}_{4}$, a single exponential function, $I=C$ $\mathrm{exp}(\ensuremath{-}\frac{\ensuremath{\omega}}{{\ensuremath{\omega}}_{0}})$, was fitted in the frequency range 5-20 ${\mathrm{cm}}^{\ensuremath{-}1}$; the density dependence of ${\ensuremath{\omega}}_{0}$ follows the scaling law derived by Fleury for rare-gas spectra. An expression involving the sum of two exponentials was fitted over a broader frequency range 5-45 ${\mathrm{cm}}^{\ensuremath{-}1}$. It is argued that the expected intensity due to the second-order dipole-induced dipole interaction or to octupole effects is too small to account for the high-frequency tail. The shape of this tail indicates that it may arise from close encounters in which the collision time is determined principally by the intermolecular potential. The values of ${\ensuremath{\omega}}_{0}$ determined from the spectra of the mixtures do not differ significantly from those obtained from pure C${\mathrm{F}}_{4}$. As the total pressure of the mixtures was varied, there were no sudden changes in the scattering analogous to the sharp increase of dielectric loss observed in the microwave absorption spectra and associated with the formation of dimers. In summary, the characteristics of the scattering closely resemble that from the rare gases.