Knowledge Bank

“The element Selenium has several interesting features with regard to molecular structure In the liquid state the molecules are supposed to be chainlike $polymers1$ which gives an analogy with liquid $sulphur2-3$. The temperature dependence of the mean chainlength gives information about the energy necessary to break such a chain and thus about the chemical binding in a chain. For the gas comparison is again possible with sulphur, quite a variety in the number of atoms per molecule being possible Analysis of gas isotherms hat given little information about the composition of the gas. It. only seems proved unambiguously that the diatomic component is always present. This diatomic component has the interesting feature that it can be in a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma$ state like $O2$ and $S2$ or in a $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma$ state. Magnetic measurements are of interest in the liquid as well as in the gas. In the liquid the magnetic measurements make it possible to count the number of free radicals (S = 1/2) at the ends of the chains and to derive the mean chainlength. In the gas, diatomic molecules in a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma$ state (S=l) will have a paramagnetic moment. As for the liquid, earlier measurements of $Busch1$ and $Risi1$ caused difficulties of interpretation. Our measurements, however, show striking differences from theirs and do not entail interpretation difficulties. They are straightforwardly in agreement with the chain theory and result in a value for the heat required to break a bond in a $chain2$ given by [ \Delta H_{5} = 20.21;Kcal/mole ] which corresponds to 0.87 eV. With respect to the gas, earlier work by $Bhatnagar7$ proved only qualitatively the of a paramagnetic diatomic component. Our quantitative results enabled us to calculate the partial vapour pressure of the paramagnetic $Se2$. These results are compared with the partial vapour pressure of all the $Se2$ as estimated by $Preuner3$, leading, as far as the measurement accuracy allows, to the conclusion that all the $Se2$ molecules are paramagnetic and thus in the $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\sigma$ state. The apparatus used was described in an earlier $paper9$ the way we obtained, the results is comparable to that followed by our previous experiments on liquid and gaseous $sulphur.3,10$”