Nuclear Isotope Shift in the Spectrum of ZnH

The structure of the lines in the (0,0) band of the band system ${}_{}{}^2{}_{}{}^{}\Pi _{\frac{1}{2}}^{}{}_{}{}^{}\to {}_{}{}^2{}_{}{}^{}\Sigma$ of zinc hydride has been studied by means of a Fabry-Perot etalon. The spectrum was excited in a hollow cathode tube. A structure caused by the isotopic constitution of zinc was observed for the lines near the head of the branch ${}_{}{}^0{}_{}{}^{}P_{12}^{}{}_{}{}^{}$. The measured shifts are larger than those calculated by the usual formulas for the vibrational and rotational isotope effects, thus showing the presence of an additional shift at least partly of nuclear origin, amounting to about 0.007 ${\mathrm{cm}}^{-1\mathrm{}}$ for the consecutive isotopes of zinc of even mass. This case is quite similar to that of the nuclear shifts in HgH, the chief differences being that they are about 10 times smaller in absolute value and in the opposite direction.