Disulfur

Disulfur is the diatomic molecule with the formula S₂. It is analogous to the dioxygen molecule but rarely occurs at room temperature. This violet gas is commonly generated by heating sulfur above 720 °C and comprises 99% of the vapor at low pressure (1 mm Hg) at 530 °C. S₂ is one of the minor components of the atmosphere of Io, which is predominantly composed of SO₂. Diatomic molecules are common containing C, O, N, and F, but for heavier elements they are often only stable at high temperatures.

Production

Disulfur results when an atmosphere of COS is irradiated with UV light using a mercury photosensitizer or when CS₂, H₂S₂, S₂Cl₂ or C₂H₄S are photolyzed. Singlet S₂ is also formed when sulfur compounds such as H₂S, PSF₃ or COS are photolyzed. S₂ can be generated by heating various organosulfur precursors.

Properties

S₂ exists in the triplet state (is a diradical, with two unpaired electrons) like O₂ and SO. It has the S-S double bond length of 189 pm, much shorter than the S-S single bonds in S₈, which are 206 pm long. In its Raman spectrum, the S-S vibrational band is observed at 715 cm⁻¹. The corresponding vibrational band of O-O is found at 1122 cm⁻¹. The S-S bond energy is 265 kJ/mol compared to 498 kJ/mol for O₂.