Unit Wavenumber Research Articles

A power spectrum analysis of granular intensity fluctuations and velocities

An exceptionally highly resolved spectrogram (obtained by W. Livingston at Kitt Peak) has been used to derive rms values for both the intensity fluctuations in the continuum and the granular velocities in the Baii line λ 5853.69 by means of the power spectrum analysis. The main results are: (1) a corrected rms value for the intensity fluctuations of 3.8%; (2) a nearly constant power level in the one-dimensional power spectrum per unit wave number within the range 0.00018–0.01 km-1 (≙34000 km-600km); (3) a corrected rms value for the granular velocities of ∼ 1 km/s.

Far-Ultraviolet Spectra of Xe and CO Adsorbed on Cooled LiF Films

The uv absorption spectra of adsorbed Xe and CO in LiF films were investigated. The P31→S10 and P11→S10 transitions of Xe were observed. These atomic absorption lines are very much broadened (1000–200 cm−1) in the adsorbed state. The bands are shifted relative to the gas phase and the magnitude of the shift is a function of the surface coverage. The shift ranges from several hundred wavenumber units to the blue for low coverages to several hundred wavenumber units to the red for high coverages. Removal of orbital degeneracy, if present, is smaller than the bandwidth. The A 1Π ← X 1Σ+ transition of adsorbed CO was investigated in the wavelength region 1600–1300 Å. The bands are quite narrow compared to the bands of adsorbed Xe. Each vibronic state is split into two components. The magnitude of the splitting is 600–1000 cm−1. This splitting is believed to be due to the removal of the π-orbital degeneracy by the LiF surface field.

A fully compensated versatile spectrofluorimeter.

A spectrofluorimeter is described which produces spectra free from all serious instrumental distortions and plots quanta per unit wave number against wave number. The correction system employed ensures reproducibility of measured intensities over periods of several weeks. An explanation of the operation of the instrument is given and some of its advantages over previously reported systems are indicated. Examples of performance are presented.

DIFFUSENESS IN ELECTRONIC SPECTRA THE VAPOR SPECTRUM OF ANTHRACENE

Approximate calculations of the number of rovibronic transitions per unit wavenumber are given for benzene, naphthalene, anthracene, and tetracene. Primarily because of the density of sequence structure all transitions in tetracene vapor should be irresolvably crowded, and hence apparently diffuse, at practical temperatures. Anthracene, whose spectrum has hitherto been described as wholly diffuse, is predicted to be capable of showing resolvable structure at room temperature. At 60 °C and 40 m path a short region of fine sharp structure has been observed. The origin of the first singlet transition is located at 27 688.3 cm−1 (27 757.6 cm−1 in anthracene-d10).

Brightness temperatures and intensity measurements in flash discharges

The brightness temperature and the intensity distribution of the Lyman, coaxial and capillary-type flash tubes have been measured and compared over the wavelength range from 2580 to 4520 Å. The brightness temperature, obtained by comparison with a standard lamp, for these flash tubes ranged from 13 000 to 30 000 °K. The intensity per unit wave number was found to be independent of wave number over the above range for the Lyman and coaxial tubes. For the capillary flash the region independent of wave number extended up to 31 000 cm -1 beyond which the continuum decreased exponentially, in agreement with the predictions of the Unsöld-Kramers theory.

The Arc Spectra of Iodine, Bromine, and Chlorine in the Schumann Region

The arc spectra of Cl, Br, and I have been investigated in the region between 2050 and 1230 A. U. Wave-length tables are given. 1396.5 and 1633.6 A. U. are the wave-lengths of the lines of longest wave-length of Cl and Br, respectively, and correspond to the previously known 2062.1 line of I. Doublet differences of 881, 3685, 7600 wave number units are found between lines of Cl, Br, and I spectra respectively and are thought to be the separations of the two levels of normal doublet $p$ states of the atoms. The probable resonance lines are of wave-lengths 1379.6, 1540.8 and 1782.9 A. U. corresponding to radiating potentials of 8.95, 8.01, and 6.92 volts. No band spectrum of HCl appeared in the region investigated although the excitation was probably favorable for its production.

A Band of Unusual Structure Probably Due to a Highly Unstable Calcium Hydride Molecule

In the spectrum of the calcium are in hydrogen at low pressure (best 3-20 mm) an isolated band occurs in association with the lines of neutral calcium. The wide spacing of the lines and the absence of appreciable isotope effect practically assure its hydride origin. The simple structure indicates a diatomic molecule. Reproductions and measurements of the lines are given. The band appears to consist of a P and an R branch with a single missing line in the middle. The two branches do not form a single series. From the abnormally weak central lines, the intensity of each branch rises to a maximum, then begins to fall slowly, until the lines are cut off sharply at the tenth line in the R and the eleventh in the P branch. These two lines both show a perturbation of -0.60 wave-number units. Assuming that these last perturbed lines have a common initial state, the band is analyzed in accordance with Kratzer's theory, applicable to molecules which have net electronic angular momentum in the plane of molecular rotation. For the initial state, the energy may be expressed by: $\frac{{E}^{\ensuremath{'}}}{\mathrm{hc}}=C+28,353.38+0.039 ({j}^{\ensuremath{'}}\ensuremath{-}\frac{3}{4})+4.798 {({j}^{\ensuremath{'}}\ensuremath{-}\frac{3}{4})}^{2}\ensuremath{-}0.000900 {({j}^{\ensuremath{'}}\ensuremath{-}\frac{3}{4})}^{4}$; for the final state, by: $\frac{{E}^{\ensuremath{'}\ensuremath{'}}}{\mathrm{hc}}=C\ensuremath{-}0.043 ({j}^{\ensuremath{'}\ensuremath{'}}\ensuremath{-}\frac{1}{2})+4.232 {({(j}^{\ensuremath{'}\ensuremath{'}}\ensuremath{-}\frac{1}{2})}^{2}\ensuremath{-}0.000192 {({j}^{\ensuremath{'}\ensuremath{'}}\ensuremath{-}\frac{1}{2})}^{4}$, where $j$ is the rotational quantum number. The last line in each branch corresponds to ${j}^{\ensuremath{'}}=11$. This limitation of the ${j}^{\ensuremath{'}}$ values, and the limitation to the value 0 of the vibrational quantum numbers ${n}^{\ensuremath{'}}$ and ${n}^{\ensuremath{'}\ensuremath{'}}$, indicated by the isolated character of the band, are explained as due to extreme molecular instability, such that the force holding the Ca and H atoms together begins to fall off very rapidly with distance if the atoms depart somewhat from their (rotationless) equilibrium position. Such a rapid falling off is possible only for a non-polar molecule. The emitting molecule is probably, then, a compound of hydrogen with an excited (not ionized) calcium atom, which may be of an unstable ${\mathrm{H}}_{2}$-like type analogous to the emitters of the Zn, Cd, Hg, Cu, Mg and other hydride bands.

Isotope Effects in the Band Spectra of Boron Monoxide and Silicon Nitride

IN 1914 Jevons1 made measurements on a band spectrum which he attributed to boron nitride. He correlated most of the bands into two systems (“” and “”); a number of weaker bands remained. Recent investigation by the writer2 shows that the spectrum—which is probably due to the compound BO—really consists of two superposed spectra.3 These are related to each other exactly as would be predicted by the quantum theory of band spectra if the more intense spectrum is due to the more abundant isotope B11O, and the less intense to the less abundant isotope B10O. Every one of the approximately 80 bands of B11O, including those both of the and of the systems, is matched, so far as can be determined4, by a corresponding B10O band of about the expected intensity.5 In each system, the central band, corresponding to an electronic change alone in a vibrationless molecule, is practically coincident for the two isotopes.6 From this centre the bands extend both toward lower and toward higher frequencies, the pattern being exactly the same for both isotopes, the scale or spacing of this pattern, however, being larger for the lighter isotope in a ratio approximately equal to the ratio of the molecular vibration frequencies. This is exactly as predicted by the quantum theory. The maximum separation between corresponding bands of the two isotopes is more than 300 wavenumber units in each system (this amounts to about 200 A. U. near 8500 in the system).