Intercollisional interference at low temperatures

1985 ◽  
Vol 63 (1) ◽  
pp. 99-103
Author(s):  
John Courtenay Lewis
Keyword(s):  
Dipole Moment ◽  
Impact Parameter ◽  
Low Temperatures ◽  
Quantum Effect ◽  
Intermolecular Force ◽  
Fundamental Band ◽  
Induced Dipole ◽  
Binary Collisions

The intercollisional interference dip in the Q-branch of the fundamental band of collision-induced spectra of H2–He mixtures partially fills in at low temperatures. In contradiction to claims that this ia a quantum effect, we show 1. that if the induced dipole moment is exactly proportional to the intermolecular force then the interference dip goes to zero at all temperatures; 2. that the filling-in of the dip is essentially a classical phenomenon and is due mainly to the discontinuity in the distance of closest approach during binary collisions as a function of impact parameter.

Intercollisional Interference in the S Lines of H2–He Mixtures

1975 ◽  
Vol 53 (10) ◽  
pp. 954-961 ◽  
Author(s):  
J. D. Poll ◽  
J. L. Hunt ◽  
J. W. Mactaggart
Keyword(s):  
Dipole Moment ◽  
Line Shape ◽  
Short Range ◽  
Experimental Results ◽  
Strength Parameter ◽  
Free Molecule ◽  
Fundamental Band ◽  
A Value ◽  
Induced Dipole ◽  
Interference Minimum

Further experimental results on the pressure induced spectrum of normal H2–He in the region of the S(1) branch of the fundamental band are presented. These results show a well-defined minimum at the transition frequency of the free molecule. The S line is found to be the sum of two components. One of these is of essentially the same nature as the Q branch and should therefore show a pronounced intercollisional interference minimum. The second component shows the usual quadrupolar line shape without a minimum. Finally, a value for the strength parameter characterizing the short range component of the induced dipole moment is determined.

Theory of Intercollisional Interference Effects. IV. Does a Zero Minimum in Induced Absorption Imply the Proportionality of the Induced Dipole Moment to the Force?

1973 ◽  
Vol 51 (23) ◽  
pp. 2455-2458 ◽  
Author(s):  
J. Courtenay Lewis
Keyword(s):  
Dipole Moment ◽  
Lorentz Gas ◽  
Intermolecular Force ◽  
Interference Effects ◽  
Induced Absorption ◽  
Induced Dipole ◽  
Interference Minimum

We show that, within the limits of the theory of intercollisional interference effects developed for collision-induced absorption by a Lorentz gas in paper I of this series, an intercollisional interference minimum which goes precisely to zero implies that the induced dipole moment is exactly proportional to the intermolecular force.

Intercollisional interference effects in pressure-induced infrared spectra

1968 ◽  
Vol 46 (10) ◽  
pp. 1173-1179 ◽  
Author(s):  
J. Van Kranendonk
Keyword(s):  
Spectral Density ◽  
Infrared Spectra ◽  
Interference Effect ◽  
Dipole Moments ◽  
Intermolecular Force ◽  
Interference Effects ◽  
Anisotropic Part ◽  
Induced Dipole ◽  
Binary Collisions ◽  
Zero Frequency

The dip observed in the Q branch of the pressure-induced vibrational spectra at high densities is shown to be an interference effect due to the correlations existing between the dipole moments induced in successive binary collisions. A similar dip is predicted to exist in the translational spectra of inertgas mixtures at zero frequency. This intercollisional interference effect has the same origin as the dip in the spectral density of the intermolecular force, discussed by Purcell in connection with nuclear electric dipole relaxation. The effect does not occur for the anisotropic part of the induced dipole moments, and this explains the observed absence of any splitting of the S lines and of the QQ component of the Q branch of the induced infrared spectra.

scholarly journals Elementary Statistical Models for Vector Collision-Sequence Interference Effects with Poisson-Distributed Collision Times

2010 ◽  
Vol 2010 ◽  
pp. 1-5 ◽  
Author(s):  
John Courtenay Lewis
Keyword(s):  
Dipole Moment ◽  
Poisson Process ◽  
Statistical Models ◽  
Intermolecular Force ◽  
Interference Effects ◽  
Arbitrary Power ◽  
Realistic Estimate ◽  
Induced Dipole ◽  
Using Data

In a recent paper (Lewis, 2008) a class of models suitable for application to collision-sequence interference was introduced. In these models velocities are assumed to be completely randomized in each collision. The distribution of velocities was assumed to be Gaussian. The integrated induced dipole moment μk, for vector interference, or the scalar modulation μk, for scalar interference, was assumed to be a function of the impulse (integrated force) fk, or its magnitude fk, experienced by the molecule in a collision. For most of (Lewis, 2008) it was assumed that μk∝fk and μk∝fk, but it proved to be possible to extend the models, so that the magnitude of the induced dipole moment is equal to an arbitrary power or sum of powers of the intermolecular force. This allows estimates of the infilling of the interference dip by the disproportionality of the induced dipole moment and force. One particular such model, using data from (Herman and Lewis, 2006), leads to the most realistic estimate for the infilling of the vector interference dip yet obtained. In (Lewis, 2008) the drastic assumption was made that collision times occurred at equal intervals. In the present paper that assumption is removed: the collision times are taken to form a Poisson process. This is much more realistic than the equal-intervals assumption. The interference dip is found to be a Lorentzian in this model.

Theory of collision-induced translational absorption

1968 ◽  
Vol 46 (10) ◽  
pp. 1163-1172 ◽  
Author(s):  
V. F. Sears
Keyword(s):  
Dipole Moment ◽  
Line Shape ◽  
Shape Function ◽  
Interatomic Potential ◽  
Exponential Model ◽  
Rare Gas ◽  
Repulsive Core ◽  
Frequency Range ◽  
Induced Dipole ◽  
Binary Collisions

A theory of the line shape for collision-induced translational absorption in rare-gas mixtures is developed. The reduced line-shape function is expanded in terms of the quantity ρ/σ, typically of the order of 0.1, where ρ is the range of the induced dipole moment and σ is the size of the repulsive core of the interatomic potential. The calculation is based on the special properties of the exponential model for the induced electric dipole moment. The temperature is assumed to be sufficiently high that the motion of the atoms can be treated classically, while the density is assumed to be sufficiently low that only binary collisions are important and intercollisional correlation effects are negligible over the frequency range of interest. A least-squares comparison of theory with experiment yields values for ρ and the magnitude of the induced moment for Ne–Ar and He–Ar pairs.

Intensity of the Pressure-Induced Fundamental Infrared Band of Gaseous Chlorine

1973 ◽  
Vol 51 (6) ◽  
pp. 696-697 ◽  
Author(s):  
P. T. T. Wong ◽  
E. Whalley
Keyword(s):  
Dipole Moments ◽  
Good Evidence ◽  
Transition Moment ◽  
Infrared Band ◽  
Fundamental Band ◽  
Induced Dipole ◽  
Integrated Intensity ◽  
Type Interaction

The integrated intensity of the pressure-induced fundamental band of gaseous chlorine measured by Winkel, Hunt, and Clouter is about 5 times that calculated assuming that the transition moment arises from the oscillation of quadrupole-induced dipole moments. This provides good evidence that valence-type interaction between gaseous chlorine molecules occurs.

DIRECTIONAL DIFFUSION OF K ATOMS ON A GaAs(110) SURFACE

2006 ◽  
Vol 05 (06) ◽  
pp. 895-900 ◽  
Author(s):  
NOBUYUKI ISHIDA ◽  
AGUS SUBAGYO ◽  
KAZUHISA SUEOKA
Keyword(s):  
Dipole Moment ◽  
Electric Field ◽  
Radial Direction ◽  
Negative Sample ◽  
Directional Diffusion ◽  
Sample Bias ◽  
Induced Dipole ◽  
High K ◽  
Scanning Area ◽  
The Relationship

We performed STM measurements on the K/GaAs (110) surface with high K coverage. The K atoms gradually disappeared while scanning the tip over the surface at negative sample bias voltage. The phenomenon strongly occurred over the scanning area and can be explained by the field-induced surface diffusion from the scanning area to radial direction. Considering the interaction between the dipole moment of the adsorbed K atoms and the electric field, we discuss the relationship between the static and induced dipole moment of K atoms on a GaAs (110) surface.

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