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15 Dec 1963

Volume 39, Issue 12, pp. 3167-3542

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Unitary Operator Formalism of the Eigenvalue Problems

Joseph C. Y. Chen

J. Chem. Phys. 39, 3167 (1963); http://dx.doi.org/10.1063/1.1734177 (4 pages) | Cited 15 times

Online Publication Date: 29 June 2004

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Utilization of the parameters involved in the system under consideration leads to a unitary operator formalism for dealing with eigenvalue problems. The existence of a unitary linear operator which transfers a known function, being predetermined for a special choice of the parameter, to the general eigenfunction is demonstrated and its properties are discussed. The related hypervirial theorems for variational Hellmann—Feynman wavefunction are discussed. The scaling problem and virial theorem are treated in some detail by means of the unitary operator techniques.

On the Density—Intensity Calibration in Electron Diffraction Studies

K. Kimura and S. H. Bauer

J. Chem. Phys. 39, 3171 (1963); http://dx.doi.org/10.1063/1.1734178 (2 pages) | Cited 7 times

Online Publication Date: 29 June 2004

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A general formulation for the dependence of the optical density on exposure in electron diffraction photographs is given, and an analytical function for the density—intensity calibration is expressed in terms of observable density data.

Electron Diffraction Study of the Molecular Structures of Sulfur Tetrafluoride (SF4) and Thionyl Tetrafluoride (SOF4)

K. Kimura and S. H. Bauer

J. Chem. Phys. 39, 3172 (1963); http://dx.doi.org/10.1063/1.1734179 (7 pages) | Cited 33 times

Online Publication Date: 29 June 2004

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The molecular structures of SF4 and SOF4 in the gaseous state were determined by electron diffraction using sector‐microphotometer data. Both molecules were confirmed to have trigonal bipyramidal structures (C2v symmetry), with two nonequivalent sets of F☒S bond distances. The bond lengths, in terms of the center of gravity parameter, rg, and the bond angles are as follows:
math
The polar F☒S☒F angles are measured along an arc which bisects the equatorial FSF angle.

Isotope Effects on Internal Frequencies in the Condensed Phase Resulting from Interactions with the Hindered Translations and Rotations. The Vapor Pressures of the Isotopic Ethylenes

Marvin J. Stern, W. Alexander Van Hook, and Max Wolfsberg

J. Chem. Phys. 39, 3179 (1963); http://dx.doi.org/10.1063/1.1734180 (18 pages) | Cited 66 times

Online Publication Date: 29 June 2004

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Interaction of the hindered translations and rotations with the internal vibrations in the condensed phase leads to isotope‐dependent shifts of the internal frequencies. This isotope dependence is a necessary consequence of the fact that the coordinates representing the translations and rotations of the molecule as a whole are, in general, isotope dependent. This external—internal interaction is investigated and the XH2 system is employed as a simple example to demonstrate the nature of the interaction. It is shown that the experimentally determined vapor pressures of the isotopic ethylenes may be rationalized when the external—internal interaction is taken into account. A force field based on a simple cell model for liquid ethylene is obtained which yields good agreement with the experimentally determined vapor‐pressure isotope effects. The force field, while not unique, fits (and is in fact partially based on) other available data on liquid ethylene.

Statistical Mechanics of Nonspherical Molecules

William A. Steele

J. Chem. Phys. 39, 3197 (1963); http://dx.doi.org/10.1063/1.1734181 (12 pages) | Cited 92 times

Online Publication Date: 29 June 2004

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A general approach to the calculation of the properties of classical fluids made up of nonspherical molecules is discussed. It is assumed that the total interaction energy is a sum of pairwise interactions which are arbitrary functions of the molecular separations and orientations. The pairwise interaction energy, and the two‐molecule correlation functions are written as series in the complete set of orthonormal functions of the molecular orientation angles, with coefficients which are functions of the distance of separation. Explicit expressions are given for the thermodynamic properties of these systems, and for the dielectric constant and rotational friction constant. Equations for the coefficients in the series for the pair correlation function are obtained by using a coupling parameter which determines the magnitude of the nonspherical part of the potential. Finally, it is shown that the number and kind of terms which appear in the series for the interaction energy and the pair correlation function are determined by the symmetry of the molecules. In this way, one can bring about a considerable reduction in the complexity inherent in the calculation of the ensemble average properties of molecules having arbitrary shapes.

Systematics of Vibrational Relaxation

Roger C. Millikan and Donald R. White

J. Chem. Phys. 39, 3209 (1963); http://dx.doi.org/10.1063/1.1734182 (5 pages) | Cited 395 times

Online Publication Date: 29 June 2004

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A large number of data points for the vibrational relaxation time (pτv in atm sec) of simple systems have been logarithmically plotted vs (T°K)—⅓. It appears that each system is well represented by a straight line, and that most of these straight lines when extended to higher temperatures intersect near the point [pτv=10—8 atm sec, (T°K)—⅓=0.03]. Systems with a small reduced mass μ are exceptions to such a simple convergence, and in an improved scheme, the location of the convergence point is dependent on the reduced mass. Such a presentation has lead to an empirical equation correlating available measurements of vibrational relaxation times: log10(pτv) = (5.0×10−4)μ½math[T−⅓−0.015μ¼]−8.00, where θ is the characteristic temperature of the oscillator in K deg. This equation reproduces the measured times within 50% for systems as diverse as N2, I2, and O2☒H2. In the worst case thus far, O2☒Ar near 1000°K, it is off by a factor of 5.

Boltzmann Equation and Inverse Collisions. II. A Model for Association and Dissociation

James T. O'Toole and John S. Dahler

J. Chem. Phys. 39, 3214 (1963); http://dx.doi.org/10.1063/1.1734183 (19 pages) | Cited 3 times

Online Publication Date: 29 June 2004

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The techniques of classical nonequilibrium statistical mechanics are applied to a gas which exhibits two distinct types of molecular interaction. The first allows chemical bonding to the extent of dimer formation; the second, impulsive in nature, provides a tractable mechanism for three‐body energy exchange. Hydrodynamic equations are derived for each of the two quasicomponents. A formal description of the reaction kinetics is developed which leads to a perturbation method for obtaining corrections to a theory based on an assumption of uniformly canonical distributions.

Statistics of Irreversible Termination in Homogeneous Anionic Polymerization

Bernard D. Coleman, Fred Gornick, and George Weiss

J. Chem. Phys. 39, 3233 (1963); http://dx.doi.org/10.1063/1.1734184 (7 pages) | Cited 6 times

Online Publication Date: 29 June 2004

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The effect of irreversible termination on the molecular weight distribution of a polymer prepared by homogeneous anionic polymerization is examined for cases in which the initiator is monofunctional and initiation is instantaneous. A general procedure for the calculation of the chain length distribution, as well as its moments, is presented. The procedure is then illustrated by an exact treatment of an isothermal batch polymerization for which we obtain the ratio rσ(t) of the weight to number average molecular weights as a function of the fraction of monomer consumed, the initial ratio σ of the terminator concentration to that of the initiator, the ratio ρ of the rate constant for termination to the rate constant for propagation, and the average degree of polymerization at time t, 〈n1〉t.
When σ is much less than unity, and the limiting number average D.P. 〈n1〉∞ is very large, rσ(t) approaches the following value as the reaction nears completion: rσ(∞) = 1+σρ(2+ρ)—1.

Separation of Gas Mixtures in Supersonic Jets

Victor H. Reis and John B. Fenn

J. Chem. Phys. 39, 3240 (1963); http://dx.doi.org/10.1063/1.1734185 (11 pages) | Cited 55 times

Online Publication Date: 29 June 2004

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The supersonic jets resulting from the free expansion of nitrogen—hydrogen mixtures from small sonic nozzles were carefully studied by means of pressure and composition probing. The apparent concentration of heavy species in the core of the jet, originally observed by others, was confirmed. The mechanism by which this separation occurs is shown to be a consequence of the presence of the probe. The deceleration occasioned by the bow shock on the probe is suggested as the cause of the separation. The previously suggested mechanism of radial migration of light species from the jet axis does not seem to be applicable to the present results.

Survey of the Spectra of the Divalent Rare‐Earth Ions in Cubic Crystals

Donald S. McClure and Zoltan Kiss

J. Chem. Phys. 39, 3251 (1963); http://dx.doi.org/10.1063/1.1734186 (7 pages) | Cited 170 times

Online Publication Date: 29 June 2004

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The rare‐earth ions may exist in the divalent state in suitable host crystals such as CaF2. All of the trivalent ions from Ce to Yb (and probably also La) are reduced in situ to the divalent state in CaF2 by gamma irradiation. The spectra of most of these ions show that the ground and first few excited states derive from fn configurations, but the weak absorption due to these is masked at higher energies by strong broad bands of the parity‐permitted fn→fn—1d transitions. The excitation energy of these spectra have been calculated in a first approximation as the energy difference between the ``Hund rule,'' single‐determinant states of the configurations fn—1d and fn. This procedure satisfactorily accounts for the remarkable variations in the excitation energy in passing from one ion to the next in the series with the exception of Gd++, Ce++, and Tb++. Gd++ probably has f7d for its ground configuration, while Ce++ and Tb++ are borderline cases. The spectral structure probably arises chiefly from the crystal‐field splitting of the d orbital, since each ion in CaF2 has a similar spectrum, and the spectra change drastically in sites of other than cubic symmetry.

Smooth Curve Approximation to the Energy‐Level Distribution for Quantum Harmonic Oscillators

Everett Thiele

J. Chem. Phys. 39, 3258 (1963); http://dx.doi.org/10.1063/1.1734187 (5 pages) | Cited 35 times

Online Publication Date: 29 June 2004

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It is pointed out that the distribution of energy levels for a set of quantum oscillators may be expressed exactly as the inverse Laplace transform of a function closely related to the quantum partition function. This observation leads quite easily to a smooth curve approximation for the energy‐level distribution which can be expressed in terms of a generalized Bernoulli polynomial. A connection between this approximation and those given by Schlag and Sandsmark and by Whitten and Rabinovitch is established. A detailed comparison with Whitten and Rabinovitch's results is made for the special case of degenerate oscillators.

Investigation of Early Ionization Processes in Shocked Xenon

D. S. Hacker and H. Bloomberg

J. Chem. Phys. 39, 3263 (1963); http://dx.doi.org/10.1063/1.1734188 (13 pages) | Cited 6 times

Online Publication Date: 29 June 2004

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Measurements of ionization rates in noble gases have been of considerable interest, with much of the recent experimental work performed at very high temperatures with shock‐tube techniques. As a result, there have been several conflicting theories formulated to trace the history of ionization phenomena. A major difficulty has been the problem of precisely identifying the earliest stage of the ionization process. Since the probability of atom—atom collisions leading to ionization is small, another source of energy sufficient to promote the necessary early stage of the process must be provided. It appears that under conditions of relatively low temperatures, as in weak shock waves, the assumption of a photoexcitation mechanism of the gas is plausible. Biberman and Veklenko have suggested such a mechanism for the production of excited states of rare gases in shock waves. This mechanism has been used to explain the initial shock‐front ionization. The nature of the processes responsible for visible emission at the shock front, which has been designated as impurity radiation, appears to be a result of the transfer of energy from the excited rare‐gas atoms to the impurity molecule.
Spectral observations of the shock zone in xenon have been made in a carefully outgassed shock tube (10—6 mm Hg). The absorption spectrum is typical of molecular fragments of carbon (C2) which has been shown earlier to be localized in the region of 4500 to 4960 Å. Calcium or sodium, usual alkali impurities, were not observed in any measurement. The emission appeared to be predominantly from the xenon and possible carbon impurities.
Microwave absorption measurements were made normal to the shock front. By use of a plasma model which assumes a linear varying electron density, microwave attenuation in the region of cutoff was measured to determine the rate of ionization and the plasma collision frequency. The observed ionization rate was of second order with respect to xenon pressure for the temperature range of 4000° to 9000°K. The observed activation energy was 1.60 eV±0.2. This was the approximate activation energy for the following reactions in xenon:
math
The experimentally determined rate expression for ionization is given as
math
Radiation at the shock front appears to be best described by the excitation of impurity or by the dissociation of Xe2 as suggested by Tanaka:
math

Analogies between Higher‐Order Analytical and Numerical Perturbation—Iteration Methods

R. A. Sack

J. Chem. Phys. 39, 3275 (1963); http://dx.doi.org/10.1063/1.1734189 (2 pages) | Cited 2 times

Online Publication Date: 29 June 2004

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An analogy is pointed out between Hirschfelder's perturbation—iteration method for the determination of eigenvalues and eigenfunctions of linear differential operators and Roothaan's numerical procedure applicable to finite matrices. An analytical procedure analogous to Ostrowski's third‐order matrix method is shown to lead to unmanageable differential equations.

Reaction between Nitric Oxide and Ozone in a Supersonic Nozzle

J. E. Marte, E. Tschuikow‐Roux, and H. W. Ford

J. Chem. Phys. 39, 3277 (1963); http://dx.doi.org/10.1063/1.1734190 (9 pages) | Cited 6 times

Online Publication Date: 29 June 2004

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The rate of reaction between nitric oxide and ozone in a supersonic nozzle was measured in the temperature range 245–345°K by following the absorption of ultraviolet radiation by ozone at 2537 Å. The specific rate constant was found to be
math
The result is in good agreement with previous studies and confirms the bimolecular nature of the reaction. The experimental pre‐exponential factor is in satisfactory agreement with one calculated from transition state theory.

Dielectric Dispersion of a Polar—Nonpolar Liquid Mixture Near the Critical Solution Temperature

R. G. Quinn and C. P. Smyth

J. Chem. Phys. 39, 3285 (1963); http://dx.doi.org/10.1063/1.1734191 (4 pages) | Cited 12 times

Online Publication Date: 29 June 2004

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The dielectric dispersion of the mixture nitrobenzene and 2,2,4‐trimethylpentane has been measured at a single concentration over a temperature range from 40°C to the temperature of turbidity and at wavelengths of 575 m, 1.26, 3.22, and 10.0 cm. It was found that the dispersion can be characterized by a single relaxation time over most of the temperature range but that a distribution of relaxation times was necessary near the critical solution temperature. The distribution was also found to broaden as the temperature was lowered. The magnitude of the relaxation time was found to tend to a maximum value as the critical solution temperature was approached. The variations of the static dielectric constant and the density were also measured and found to exhibit the usual maxima. The data obtained are discussed in a qualitative manner in terms of cybotactic regions existing within the liquid and similarities between the dielectric and structural relaxation processes are pointed out.

Upper and Lower Bounds for Ground‐State Second‐Order Perturbation Energy

Stephen Prager and Joseph O. Hirschfelder

J. Chem. Phys. 39, 3289 (1963); http://dx.doi.org/10.1063/1.1734192 (6 pages) | Cited 30 times

Online Publication Date: 29 June 2004

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The first‐order perturbation equation, using the Dalgarno—Lewis formulation, is arranged in a form analogous to the Poisson equation for the electrostatic potential produced by a charge distribution in a medium of variable dielectric constant. Thus, the Thomson and Dirichlet variational principles of electrostatics can be used to obtain approximate solutions to the first‐order perturbation equation for systems in either the ground state or the lowest energy state of a given symmetry. The Thomson principle provides a useful lower bound to the second‐order perturbation energy. The Dirichlet principle is derivable from the Rayleigh—Ritz or Hylleraas principles and gives an upper bound to the second‐order energy. For excited states, the Sinanoğlu principle provides the upper bound. By optimizing the scaling of the trial perturbed wavefunction, the Hylleraas principle is presented in a somewhat improved form. As an example, the polarizability of atomic hydrogen is used to illustrate both the Thomson and Dirichlet principles and to place upper and lower bounds on the polarizability.

Polyhedral Clathrate Hydrates. V. Structure of the Tetra‐n‐butyl Ammonium Fluoride Hydrate

R. K. McMullan, M. Bonamico, and G. A. Jeffrey

J. Chem. Phys. 39, 3295 (1963); http://dx.doi.org/10.1063/1.1734193 (16 pages) | Cited 50 times

Online Publication Date: 29 June 2004

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The structure of (n‐C4H9)4N+F—⋅32.8 H2O is tetragonal, of space group P42/m with the unit‐cell dimensions a=23.52 Å and c=12.30 Å. The clathrate host structure is similar to that of the (n−C4H9)4N+C6H5−COO−⋅39.5H2O and consists of a tetragonal pseudo body‐centered arrangement of groups of five face‐sharing pentagonal dodecahedra interlinked by tetrakaidecahedra and pentakaidecahedra. Whereas in the benzoate there are four salt molecules per unit cell, in the fluoride there are five. This difference in the number of guests accommodated in essentially the same host structure is possible because the four tetrakaidecahedra occupied by the benzoate groups are available for the four alkyl groups of the additional cation. In the fluoride hydrate, four of the cations have the central N+ atom at the fourfold positions (j) and that of the fifth is disordered over the twofold position (f). Thus the structure has lower symmetry than the benzoate hydrate, which is P42/mnm by reason of the disorder of the four cations over eightfold positions.
The fluoride ions replace water molecules in the host lattice, with F—⋅⋅⋅O distances of 2.80 to 2.87 Å forming an anionic host lattice. As in the other clathrate hydrate structures of this type, some of the pentagonal dodecahedra which are distorted by the presence of the cations are occupied by a guest species presumed to be additional water molecules.

Polyhedral Clathrate Hydrates. VI. Lattice Type and Ion Distribution in Some New Peralkyl Ammonium, Phosphonium, and Sulfonium Salt Hydrates

Gezina Beurskens, G. A. Jeffrey, and R. K. McMullan

J. Chem. Phys. 39, 3311 (1963); http://dx.doi.org/10.1063/1.1734194 (5 pages) | Cited 14 times

Online Publication Date: 29 June 2004

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The crystal data and preparation are discussed for 22 new peralkylated ammonium, phosphonium, and sulfonium salt hydrate crystals. Although these structures have not been determined in detail, it is possible to classify them according to the host‐lattice type and to draw conclusions by analogy with known structures concerning the order and disorder in the distribution of the cations and anions with respect to the water lattice.

Forces in Molecules. III. Analysis of an Empirical Potential Function

William L. Clinton and Sandra D. Frattali

J. Chem. Phys. 39, 3316 (1963); http://dx.doi.org/10.1063/1.1734195 (6 pages) | Cited 1 time

Online Publication Date: 29 June 2004

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The oscillating potential function reported in Part II of this series is analyzed in detail for all diatomic molecules for which sufficient experimental data exist. The potential function is calculated and compared to the experimental curve for several internuclear positions on either side of the equilibrium position. Criteria are given for determining the region of usefulness of this function. Some further discussion of the possible physical significance of the oscillating potential is also included.

Hyperfine Electron Spin Resonance Spectrum of the NH2 Free Radical

Brian T. Sutcliffe

J. Chem. Phys. 39, 3322 (1963); http://dx.doi.org/10.1063/1.1734196 (5 pages) | Cited 9 times

Online Publication Date: 29 June 2004

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The unrestricted Hartree—Fock method in the LCAO—MO approximation is used to calculate the coupling constants for nitrogen and hydrogen in the NH2 free radical. Both Slater and self‐consistent field orbitals are used as basis functions. The effect of a spin annihilator after energy minimization, and the effects of ``freezing'' the nitrogen core are examined. The results are compared with those obtained in a recent configuration interaction calculation; and with the experimental results.

Polymer Segmental Motion as Related to Hindered Rotation

W. W. Brandt

J. Chem. Phys. 39, 3327 (1963); http://dx.doi.org/10.1063/1.1734197 (8 pages)

Online Publication Date: 29 June 2004

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The rotational oscillational motions of small units of the polymer chain with respect to their nearest neighbors are investigated insofar as these oscillations may be responsible for the over‐all motions or configurational changes of the chain molecules. It is assumed that each degree of freedom involved in the over‐all motion is endowed with an energy given by a Boltzmann distribution and independent of the energies of its neighbors. Using mathematical results of Kac, an expression for the average ``jump'' frequency, that is, the frequency of occurrence of deflections of a critical magnitude, is obtained. This jump frequency is found to be strongly dependent on the criterion adopted for a successful jump, and on the number of degrees of freedom in the moving segment, or the segment size. There is an optimum segment size which increases with the required jump magnitude, in agreement with experiment. The temperature dependence of the jump frequencies is qualitatively correct. The results show that bond stretching and bond‐angle distortions contribute little to the over‐all configurational change, and even the nearly free rotation of chain units with large energies is of relatively minor importance (at 298.2° and 398.2°K, for polyethylene). The exact shape of the potential of hindered rotation near its minima and the type of subsidiary (gauche) minima present, on the other hand, affect the rate process very much.

Microwave Spectrum of Methyl Isocyanate

R. F. Curl, V. M. Rao, K. V. L. N. Sastry, and Jimmie A. Hodgeson

J. Chem. Phys. 39, 3335 (1963); http://dx.doi.org/10.1063/1.1734198 (6 pages) | Cited 16 times

Online Publication Date: 29 June 2004

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The J0→1 and J1→2 a‐type transitions of CH3NCO and CD3NCO have been studied. These transitions are complicated by the population of a number of internal rotation states. Several absorptions arising from the lowest energy internal rotation states have been assigned. The barrier to internal rotation of the methyl group in CH3NCO has been found to be 49±3 cal/mole from the splitting of the J3→4, K=±1, m=±3 transition by the barrier. The component of electric dipole moment parallel to the a axis has been found to be 2.81±0.06 D by measurement of the Stark effect. The nitrogen quadrupole coupling constant has been found to be eqQ=+2.3 Mc/sec.

Effect of Additives on the Ionic Reaction Mechanism in the Radiolysis of Methane

P. Ausloos, S. G. Lias, and R. Gorden

J. Chem. Phys. 39, 3341 (1963); http://dx.doi.org/10.1063/1.1734199 (8 pages) | Cited 19 times

Online Publication Date: 29 June 2004

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This work describes the reactions of the ions C2H5+ and CH5+ with C3D8, C4D10, C5D12, as well as the reactions of C2D5+ and CD5+ with C3H8. It is shown that ethyl ions undergo a hydride transfer reaction with all higher hydrocarbons even though they are present at a concentration of only 0.01%. The scavengers NO and O2 react with ethyl ions effectively, provided the relative concentration of the higher hydrocarbons is less than that of the free radical scavengers. A proton‐transfer reaction between CH5+ and higher hydrocarbons followed by a rapid decomposition of the protonated hydrocarbon into a carbonium ion and a neutral alkane molecule is shown to occur. From the data it can be deduced that at a methane pressure of 48 cm G(C2H5+) =0.9±0.2 and G(CH5+) =1.9±0.2. It is concluded that in earlier published studies of the radiolysis of methane, the C2H5+ and CH5+ ions reacted with the accumulated products or with the added free radical scavengers, thus excluding the neutralization of these two species.

Temperature and Pressure Dependence of the Co59 Nuclear Resonance Chemical Shift

George B. Benedek, Robert Englman, and John A. Armstrong

J. Chem. Phys. 39, 3349 (1963); http://dx.doi.org/10.1063/1.1734200 (15 pages) | Cited 25 times

Online Publication Date: 29 June 2004

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We have measured with precision the temperature and pressure dependence of the Co59 nuclear resonance chemical shift (σ) in the octahedral cobalt complexes Co(NH3)63+, Co(CN)63—, and Co(NO2)63— in aqueous solution. The pressure and temperature range was 1 to 10 000 kg/cm2 and 3° to 80°C, respectively. From the pressure dependence of σ and a theoretical determination of the compressibility of the complexes we have deduced the dependence of the crystal‐field splitting on the cobalt—ligand distance. A theory for the explicit temperature dependence of the chemical shift is presented. The fundamental parameters which enter the theory are the 15 normal mode frequencies when the cobalt electrons are in the ground state and when they are in the excited state. While the former quantities are known from the vibrational spectra of these complexes, the latter are unknown. By fitting the theory to the experimental data, one concludes that on the average the vibration frequencies in the 1T1g excited electronic state must be smaller than those in the ground state by about 30% for the cyanide and nitrite complexes and by about 20% for the ammonia complex. A nonlinear dependence of σ on the temperature is predicted by the theory and observed experimentally.

Photoconduction in Charge‐Transfer Complexes

H. Akamatu and H. Kuroda

J. Chem. Phys. 39, 3364 (1963); http://dx.doi.org/10.1063/1.1734201 (5 pages) | Cited 9 times

Online Publication Date: 29 June 2004

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The photoconduction in the solid molecular complexes of pyrene with tetracyanoethylene, bromanil, and 1,3,5‐trinitrobenzene has been observed. In each case, the intrinsic photoconduction arises with photon energy a little higher than the energy gap for the excitation to the conduction state, while its spectral region does not coincide with the charge‐transfer band in the electronic spectrum. It has been suggested that in these ``weak'' charge‐transfer solid complexes, the excited state associated with the charge‐transfer band cannot contribute to conduction, and an energy diagram for the electronic state in these crystals has been proposed.
A structure‐sensitive secondary photoconduction has been observed in the spectral region around the threshold of the charge‐transfer band, which is likely due to the interaction between charge‐transfer excitons and imperfections in the crystal.
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