Nuclear Isotope Shift in the Spectra of HgH+and HgD+

Abstract

The structure of the lines in the band spectra of Hg${\mathrm{H}}^{+}$ and Hg${\mathrm{D}}^{+}$, excited in a hollow cathode tube, is studied with Fabry-Perot etalons. The lines are found to be broadened, with traces of structure, an effect caused by the isotopic constitution of mercury. The structure shows that there is no anomalous behavior of components belonging to the odd Hg isotopes due to hyperfine splitting, but the half-widths of the lines differ widely from the expected ones. From the measured half-widths the shifts between the consecutive even isotopes of Hg are evaluated and then the differences between these and the values obtained from the formulas for the normal vibrational and rotational isotope effect calculated. These additional shifts show the same behavior as the shifts found some years ago in HgH and HgD and therefore must be explained as nuclear isotope shifts, that is, shifts connected with differences in nuclear volume of the different isotopes of Hg. For the lowest vibrational bands the shifts are of the same sign as in HgH, but decrease with the vibrational energy of both upper and lower states, changing sign for sufficiently high vibrational energies and probably tending in the limit of dissociation to the shifts found in the corresponding quadrupole line 2815A of Hg II. Consideration of the data on the nuclear isotope shifts in HgH, Hg${\mathrm{H}}^{+}$, Hg I and Hg II permits some conclusions about the deformation of the electron clouds in Hg and ${\mathrm{Hg}}^{+}$ caused by the attachment of a hydrogen atom, and a rough calculation of the nuclear shifts in the molecular levels of HgH and Hg${\mathrm{H}}^{+}$.