## Abstract

The highly perturbed spectra of the A$^1\sum$-X$^1\sum$ systems of the silver hydride and deuteride molecules are explained in terms of an anomalous rotationless potential curve for the A state. While this curve will explain the irregularity of the vibrational interval it is necessary to include the rotational energy term $U(r)_J = U(r)_0 + (8\pi^2/\mu) J(J+1)/r^2,$ in order to explain the intensity distribution. The potential curves derived have meaningful quantum numbers, in direct contrast to the explanation of Gero & Schmid (1943). The perturbation is due to the interaction between the $^1\sum$ states formed by addition of a hydrogen atom to the $^2$P and $^2$D configurations of the silver atom. The dissociation energies of other silver-containing diatomic molecules are discussed. A partial analysis of the AgD spectrum yields the following constants in cm$^{-1}$: \begin{align*} X^1\sum^+\quad G_{(v)} &= 1250\cdot9(v+\frac{1}{2})-17\cdot2(v+\frac{1}{2})^2+0\cdot15 (v+\frac{1}{2})^3-0\cdot025(v+\frac{1}{2})^4,\\ B_{(v)} &= 3\cdot258- 0\cdot073(v+\frac{1}{2}),\\ D_{(v)} &= 8\cdot2 x 10^{-5};\\ A^1\sum^+\quad G_{(v)} &=29911\cdot3+1101\cdot5(v+\frac{1}{2})-40\cdot7(v+ \frac{1}{2})^2-1\cdot8(v+\frac{1}{2})^3,\\ B_{(v)} &= 3\cdot163 - 0\cdot124(v+\frac{1}{2}) - 0\cdot0038(v+\frac{1}{2})^2,\\ D_{(v)} &= 9\cdot0 x 10^{-5}+1\cdot7 x 10^{-6}(v+\frac{1}{2});\end{align*} where the constants for the A state are only valid for v < 5, J < 25, as the violent perturbation observed in the hydride is again present.

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