Absorption Spectrum of the Argon Molecule in the Vacuum-uv Region

The absorption spectrum of diatomic argon has been investigated in the 780–1080‐Å region with a 6.65‐m normal incidence vacuum spectrograph using the helium and argon continua as background sources. Nine discrete band systems are identified. The present analysis shows that the ground state is stable, has a dissociation energy $D_0^0\text{\hspace{0.17em}=\hspace{0.17em}76.9}{\mathrm{cm}}^{\text{−1}}$ , and six vibration levels, $\text{υ\hspace{0.17em}=\hspace{0.17em}0–5}$ . A number of previous calculations of intramolecular potentials agree with these experimental results. Definite dissociation products are assigned for some of the upper states of these systems. State designations, stabilities, and transitions from the ground state are discussed by analogy with an earlier study of the xenon molecule. In some of the upper states, the existence of potential humps (for which no definitive explanation is yet known) is demonstrated by the assignment of transitions to bound molecular states above the dissociation limits and by the onset of diffuseness in band progressions. The origin of the vacuum‐uv argon emission continuum and of other emission features is discussed in relation with the observed absorption band systems.