CHEMICAL EFFECTS ON K-X-RAY SPECTRUM

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CHEMICAL EFFECTS ON K-X-RAY SPECTRUM

K. Taniguchi, T. Mukoyama, H. Adachi

To cite this version:

K. Taniguchi, T. Mukoyama, H. Adachi. CHEMICAL EFFECTS ON K-X-RAY SPECTRUM. Journal

de Physique Colloques, 1987, 48 (C9), pp.C9-757-C9-760. �10.1051/jphyscol:19879131�. �jpa-00227241�

JOURNAL D E PHYSIQUE

Colloque C9, suppli5ment au n012, Tome 48, dbcembre 1987

CHEMICAL EFFECTS ON K-X-RAY SPECTRUM

K. TANIGUCHI, T. MuKOYAP~A* and H. ADACHI* '

Department of Solid State Electronics, Osaka Electro-

Communication University. ~atsu-Machi, Neyagawa, Osaka 572, Japan

" ~ n s t i t u t e for Chemical Research, Kyoto University, Yoshida, Kyoto 606, Japan

yogo go

Chemical effects on K-x-ray spectrum have been

studied both experimentally and theoretically. The K-x-ray spectra of various chemical compounds of Mn and Cr were measured with a double crystal spectrometer with high energy resolution.

The theoretical calculations of the K-x-ray energies and

intensities were made by the use of the discrete-variational Xa moleculer orbital method. The experimental spectra are compared with the calculated ones and the dependence of the spectrum and the KB /Ka x-ray intensity ratios on the chemical form of the compounds is descussed.

1. INTRODUCT JON

It is well known that x-ray spectra depend on the chemical surroundings of the atom [l] and extensive experimental studies for the chemical effects on the KB /Ka x-ray intensity ratios of 3d transition elements have been reported [ 2 1 . However, these KB /Ka experiments were performed solid-state x-ray detectors and KB composite x-ray peaks could not be resolved due to poor energy

resolution. On the other hand, several theoretical estimations of the chemical effects on the x-ray intensity ratios have been made, but they were based on many simplifying assumptions.

Recently we measured the KB /Ka ratios for some compounds of Cr and Mn by a high-energy resolution spectrometer [ 3 ] . The results Were

compared with the more realistc theoretical values obtained by us [ 3 1 using the molecular orbital (MO) model and found to be in qualitative

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19879131

JOURNAL DE PHYSIQUE

agreement with the calculated values. In the present work, we have measured the K-x-ray spectra and the KB / ~ a ratios for Cr and Mn compounds more accurately and compared the experimental results with the theoretical calculations in more detail.

2.EXPERIMENTAL

The measurements of K-x-ray spectra were performed by a simple quasi-two-crystal spectroscopic method [ 4 1 . The x rays from the target sample excited by an.x-ray tube were analyzed by a flat crystal and detected with a gas-flow proportional counter. The counter was scanned by O.Olo of 2 6 in Bragg angle, by means of the step scanning method. The measured spectrum was converted into an energy scale, after various corrections were made [ 5 ] . The KB /Ka intensity ratios was determined from the ratio of the areas of the KB and Ka x-ray region.

3.COMPUTATIONAL METHOD

The theoretical calculations for the K-x-ray intensities were made by the use of the discrete-variational Xa (DV-Xa ) MO method 161.

For simplicity, we assumed that all the compounds are the cluster with the tetrahedral (Td) or octahedral (Oh) symmetry, in which the central metal atom is surrounded by four or six ligand atoms. In the case of Mn metal, seven Mn atoms were assumed to be located in the D3h

symmetry. The x-ray emission rate was obtained in the dipole approximation directly from the MO wave functions using the DV integration scheme.

E N E R G Y ( 8 V ) E N E R G Y (.V)

Fig. 1. The experimental and theoretical KB x-ray emission spectra of Cr in KnCrOr, fa) and Mn in KMnOl, (b). The energy scale is adjusted to the experimental data at the KB1 , 3 line.

RESULTS

In Fig. l(a), the experimental K B x-ray spectrum of Cr in K2CrOb is compared with the calculated one. The energy scale is normalized to the experimental data at KB,,, Line. The theoretical spectrum shape was assumed to be a Lorentzian function. Figure l(b) shows a similar comparison for Mn.in KMnOt,. It can be seen from the figures that the experimental spectra are in good aqreement with the

theoretical ones.

As has been discussed in our ~revious paDer [ 3 ] , the absolute values of the calculated KO /Ka x-ray intensity ratios for Cr and Mn are in general smaller than the exuerimental data because of

Table 1. Relative KB /Ka intensity ratios for Cr (relative to KzCrO4)

Compound Symmetry Theory Experiment

Cr203 oh

CrO Td

KzCez07 Td

CrC13 6H2O Oh

CrO Oh

CrC1 Oh

Table 2. Relative kB /Ka intensity ratios for Mn (relative to KMnOt,)

.

Compound Symmetry Theory Experiment

$InCl2 .2H20 Mn0

K2MnOs IlnO MnS Mn metal

C9-760 JOURNAL DE PHYSIQUE

neglection of the exchange and overlap effects. Therefore, we compare the theoretical relative KB /Ka ratios with respect to a standared compound with the experimental results. As for the stndard,we use K ~ C ~ O Q . for Cr and KMnOs for Mn. The theoretical and experimental relative KB /Ka x-ray intensity ratios for Cr are listed in Table 1 and compared with each other. A similar comparison for Mn is also made Table 2.

It is clear from the tables that the K$ /Ka ratios of the

compounds in the Td symmetry are generally larger than those in the Oh

~~RUtIetry. The value for Xn metal is between these two values. Except for Cr03, the calculated results are in qualitative agreement with the experimental data.

In conclusion, we have measured the K-x-ray spectra from various chemical compounds of Cr and Mn with a high-energy resolution spectrometer and calculated the x-ray intensities by the use of the DV-Xa method. The experimental spectra agree well with the

theoretical ones. The measured KB /Ka intensity ratios are in qualitative agreement with the calculater values. These results indicate that the DV-Xa method is very useful to interprete the chemical effects on the K-x-ray spectra.

References

[l] Meisel A., Leonhardt G., and Szargen R., "Rontgenspektren und Chemische Bindung", (Geest & Portig, Leipzig), 1977.

[21 Brunner G., Nagel M., Hartmann E . , and Arndt E., J. Phys.

(1982) 4517 and references therein.

[3] Mukoyama T., Taniguchi K., and Adachi H., Phys. Rev.

(1986) 3710.

[ 4 ] Taniguchi K., Rev. Sci. Instrum.

54

[5] Henke B.L., and Taniguchi K., J. Appl. Phys.

47

[6] Adachi H., Tsukada M., and Satoko C., J. Phys. Soc. J p n z (1978) 875.