scholarly journals The Collision Broadening of Spectral Lines

1968 ◽  
Vol 21 (1) ◽  
pp. 13 ◽  
Author(s):  
RW Parsons ◽  
VI Metchnik ◽  
RJ Dyne
Keyword(s):  
Collision Cross Section ◽  
Hard Spheres ◽  
Spectral Lines ◽  
Line Broadening ◽  
Collision Broadening ◽  
The Mean ◽  
Gas Molecules ◽  
Collision Processes ◽  
Half Power ◽  
Van Vleck

The shape of a collision-broadened spectral line depends on the assumptions made about the collision processes involved. If the collision cross section varies inversely as the relative speed of the colliding molecules, the half-width to the half-power points and to the points of steepest slope should be 1/27T1' and 1/(2";3)7T1' respectively, where l' is the mean interval between line-broadening collisions. It is shown that, in a gas of "hard-sphere" molecules, the shape of the line is modified and the above half-widths are reduced by' 6�4 and 9�7% respectively. While it is not suggested that gas molecules behave entirely as hard spheres, it is suggested that some deviations from the Van Vleck-Weisskopf-Lorentz shape may occur, and that it may be possible to detect these deviations experimentally

Gas ionization by focused laser beams

1984 ◽  
Vol 62 (10) ◽  
pp. 1010-1013 ◽  
Author(s):  
A. L. de Brito
Keyword(s):  
Laser Radiation ◽  
Photon Energy ◽  
Ionization Energy ◽  
Laser Beams ◽  
Line Broadening ◽  
Gas Ionization ◽  
The Mean ◽  
Gas Molecules ◽  
Focused Laser Beams

It is shown that the effect of line broadening by focusing may contribute considerably to the observed laser-induced ionization of gases even when the ionization energy of the gas molecules is well above the mean photon energy of the laser radiation.

Excess entropy of the systems of molecules differing in size and shape

1983 ◽  
Vol 48 (1) ◽  
pp. 192-198 ◽  
Author(s):  
Tomáš Boublík
Keyword(s):  
Equation Of State ◽  
Hard Spheres ◽  
Excess Entropy ◽  
Convex Bodies ◽  
Pure Substance ◽  
Liquid Equilibrium ◽  
Simple Rules ◽  
Different Shapes ◽  
The Mean

The excess entropy of mixing of mixtures of hard spheres and spherocylinders is determined from an equation of state of hard convex bodies. The obtained dependence of excess entropy on composition was used to find the accuracy of determining ΔSE from relations employed for the correlation and prediction of vapour-liquid equilibrium. Simple rules were proposed for establishing the mean parameter of nonsphericity for mixtures of hard bodies of different shapes allowing to describe the P-V-T behaviour of solutions in terms of the equation of state fo pure substance. The determination of ΔSE by means of these rules is discussed.

The Use of the Pseudo-Voigt Function in the Variance Method of X-ray Line-Broadening Analysis

1997 ◽  
Vol 30 (4) ◽  
pp. 427-430 ◽  
Author(s):  
F. Sánchez-Bajo ◽  
F. L. Cumbrera
Keyword(s):  
Crystallite Size ◽  
Original Form ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Stabilized Zirconia ◽  
X Ray ◽  
Variance Method ◽  
The Mean ◽  
Voigt Function

A modified application of the variance method, using the pseudo-Voigt function as a good approximation to the X-ray diffraction profiles, is proposed in order to obtain microstructural quantities such as the mean crystallite size and root-mean-square (r.m.s.) strain. Whereas the variance method in its original form is applicable only to well separated reflections, this technique can be employed in the cases where there is line-profile overlap. Determination of the mean crystallite size and r.m.s. strain for several crystallographic directions in a nanocrystalline cubic sample of 9-YSZ (yttria-stabilized zirconia) has been performed by means of this procedure.

Echoes and imaging in solids

1990 ◽  
Vol 333 (1632) ◽  
pp. 427-439 ◽  
Keyword(s):  
Spin Echo ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Spectral Lines ◽  
Line Broadening ◽  
Rf Pulses ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
Bandwidth Limitation ◽  
Successful Approach

The broad spectral lines usually encountered in solid state NMR present considerable difficulties for imaging. One successful approach to the problem is to artificially narrow the line by multipulse or sample spinning methods. An alternative is to apply sufficiently large magnetic field gradients that they dominate the line broadening and seek ways to deal with bandwidth and power requirements thereby introduced. This paper explores the second route and demonstrates that spin-echo techniques help to solve several of the inherent problems. Gradient echoes produced by periodic reversal of the field gradients have significant advantages. The addition of synchronous RF pulses can produce an extended train of ‘solid’ echoes which overcomes, at least to some extent, the bandwidth limitation of this approach and permits rapid imaging in two dimensions. Slice selection and three-dimensional back projection have also been achieved in solid-like samples. Comparison with linenarrowing methods and relative advantages of the different approaches are addressed.

scholarly journals Internal structure and rotation of the Sun: First results from the MDI data

1997 ◽  
Vol 181 ◽  
pp. 203-210
Author(s):  
A.G. Kosovichev ◽  
J. Schou ◽  
P.H. Scherrer ◽  
R.S. Bogart ◽  
R.I. Bush ◽  
...  
Keyword(s):  
Thin Layer ◽  
Spectral Lines ◽  
Convective Boundary ◽  
Doppler Imager ◽  
Lower Amplitude ◽  
Oscillation Modes ◽  
First Results ◽  
Sharp Variation ◽  
The Mean ◽  
Initial Results

The Medium-l Program of the Michelson Doppler Imager (MDI) instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to ∼ 300. The initial results show that the noise in the Medium-l oscillation power spectrum is substantially lower than in ground-based measurements. This enables us to detect lower amplitude modes and, thus, to extend the range of measured mode frequencies. The MDI observations also reveal the asymmetry of oscillation spectral lines. The line asymmetries agree with the theory of mode excitation by acoustic sources localized in the upper convective boundary layer. The sound-speed profile inferred from the mean frequencies gives evidence for a sharp variation at the edge of the energy-generating core. In a thin layer just beneath the convection zone, helium appears to be less abundant than predicted by theory. Inverting the multiplet frequency splittings from MDI, we detect significant rotational shear in this thin layer.

Exact solution of the mean spherical model for charged hard spheres in a uniform neutralizing background

1973 ◽  
Vol 58 (10) ◽  
pp. 4171-4174 ◽  
Author(s):  
R. G. Palmer ◽  
J. D. Weeks
Keyword(s):  
Exact Solution ◽  
Hard Spheres ◽  
Spherical Model ◽  
Mean Spherical Model ◽  
The Mean ◽  
Charged Hard Spheres
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