Analysis of vibrational structure. —The electronic band system of AgCl extending from $\lambda 3124$ to $\lambda 3400$ has been obtained in emission and absorption, the latter under high dispersion. A complete vibrational quantum analysis has been carried out, giving the following formula for the heads of the bands of the molecule ${\mathrm{Ag}}^{107}$${\mathrm{Cl}}^{35}$: $\nu =31574.4+275.0\mathrm{}{v}^{\prime }-6.20\mathrm{}{v}^{\prime 2}-0.130\mathrm{}{v}^{\prime 3}-342.4\mathrm{}{v}^{\prime \prime }+1.163\mathrm{}{v}^{\prime \prime 2}$

The data give $\omega _e^{}{}_{}{}^{\prime }=343.6\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\omega _e^{}{}_{}{}^{\prime }=281.0\mathrm{}$, and ${\nu }_e=31606.9\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. Vibrational quantum numbers have been assigned to Franck and Kuhn's data for AgBr and AgI.

Isotope effects. —The vibrational isotope effect was observed for both the Cl and the Ag atoms. The complete spectrum consists of four overlapping systems due to the four possible isotopic molecules. The order of magnitude of the isotope shift for the Cl isotope effect was 1 to 30 ${\mathrm{cm}}^{-1\mathrm{}}$; for the Ag isotope effect, 1 to 4 ${\mathrm{cm}}^{-1\mathrm{}}$. The agreement of observed shifts with those calculated from the equations recently derived by Birge (not yet published) is close.

Energies and products of dissociation. The heats of dissociation of the AgCl molecule are $D_0^{}{}_{}{}^{\prime \prime }=3.11\mathrm{}$ volts in the normal state, $D_0^{}{}_{}{}^{\prime }=0.31\mathrm{}$ volt in the excited state. The energy of excitation of the atoms resulting by dissociation from the excited state is 1.10±0.12 volt. This value can be explained if it is assumed that ${}_{}{}^2{}_{}{}^{}D_{}^{\prime }{}_{}{}^{}$ states exist in Ag as in Cu and Au. It is concluded that the silver halides dissociate from the excited state into a silver atom in a ${}_{}{}^2{}_{}{}^{}D_{}^{\prime }{}_{}{}^{}$ state and a halogen atom in the metastable ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ state.

• Received 10 March 1930

DOI:https://doi.org/10.1103/PhysRev.35.960