investigation of the crystal structure of tetram-

As a tool to determine the position of the central image, the spectrum is from a given. The value of c0 as determined from this data is A. The 0 identity distance along c as calculated by means of the Polanyi formula, s). The chlorine atoms must be placed in one of the sets of four equivalent positions or in two of the three available sets of two equivalent positions (b), (c), and.

Also, these atoms cannot exist in two of the sets (b),(c) and (d), because in this case they would not contribute to the structure factor for faces with h+k odd. Of the sets of two equivalent positions (b), (c) and (d) available for the oxygen, the possibility (b) can be excluded because it does not yield enough. We can use the intensity data from oscillation photographs taken from each prism face with the c-axis vertical to determine the value of the single chlorine parameter.

The most serious of the several minor discrepancies appearing in the data from 'l'able IV is found for planes (680) and (8.10.0). Thus, it was not possible to find a single value of the parruneter that was in the range 0.275 to 0.292 for which the calculated values of SCl f or both (680) and (8 10 0) are in agreement with the experimental observations that these quantities are small negative numbers. The best agreement seems to be obtained for values of ucl in the upper part of the range and so we place uCl = O at this point.

As a factor of safety, a temperature correction was omitted in the calculation of the values of the structure tactors, but the Lorentz and polarization factors were included. If the nitrogen parameters in turn are given the limiting values of the ranges just established, we find the following chlorine-ammonia separations when uCl = 0. In the latter case, four of the ammonia groups are separated from the chloride ion with a distance smaller than the NH4 -Cl separation and since these four ammonia molecules decrease closer to the chloride ion than uN.

It is likely that v~ has a value in the mid-range of 0.000 to 0.044 and, as a result, all eight ammonia molecules. It will be assumed that for each value of uc1 each ammonia molecule of the. The data for IIIO) has been omitted because the crystal did not intercept the entire beam at this plane.

In the right half of the space below each plane is given the calculated intensity value of that plane divided by one thousand and in the other half is the observed intensity which is visually. It was assumed that each ammonia of the surrounding octets is equidistant from the chlorine atom, but x-ray data can only show that this condition is approximately satisfied. If the water molecules were placed in the plane of the chlorine atoms, we would get a minimum.

It can be seen from Figure 3 that the unity of two molecules arises from small rotations of the square configurations of ammanium oxide molecules and chlorine atoms about axes parallel to c.

Table IB. Spectral data from lllO) with [jlo ] vertical.

437 The only planes giving first-order reflection in the two Laue photographs were those with all odd indices, so the structure can be assumed to be based on a face-centered lattice. Only orders of (111) were used, the intensity calculated for (nnn) was obtained as follows. The structure factor calculated from the /0 values of Pauling and Sherman1) for the given value of. The if factor; enters since if a horizontal slit system is used, the fraction of the total beam intercepted by the strongly absorbing crystal when in the reflecting position is proportional to sin e and thus to n.

Since the temperature factor was not included, only the intensity disparities were used for which a plane with a given d11,.11 value was observed to reflect more strongly than another. Thus, since (555) is observed to reflect more strongly than (333), only those values of n for which S555 is calculated to be greater than S333 are possible. Intensity disparities appearing in the Laue pictures were used to further limit the possible range of values for the parameter.

1 + cos2 9 fJ)}. sons, except for the omission of the factor l' n and. inequalities of intensity were used between planes reflecting in the first order with very nearly the same value of n} and with a plane of a given d,u reflecting more strongly than the other with a larger d111,1. The omission of temperature, polarization, and Lorentz corrections served as a safety factor in such comparisons. The curves used for the Laue comparisons are plotted in Figure 2 and the intensity data are listed in Table II.

The intensity inequalities from Table II used and the range of values they allow for the parameter are as follows: The corresponding separation of selenium and bromine is A. Subtracting the value of the normal bond radius of the electron pair of bromine1), 1,HA gives a value of 1.40A for "octahedral " electron pair bond radii for tetravalent selenium. He found 0.24 to 0.2:) as a possible range of bromine parameter values, with the range for adequate selenium-bromine separation being 2.51 to 2.63 A, which includes the range we found.

Subtracting the normal raclius of the electron pair bond of bromine, '1.1'1 Å, from the sclenium-bromine separation, 2.54 Å, the "octahedral" radius of the electron pair bond of tetravalent selenium was found to be JAO A. variation function somewhat similar to that applied by Rosen to I-I is used in discussing the normal state of !-£,+. To see to what extent this method of treatment of molecules would be expected to be satisfactory in other cases, and whether or not a pronounced improvement could be obtained by varying the ratio of the effective nuclear charges.