Spectrum of N3— in Solution

The electronic absorption spectrum of N3— in solution was investigated. For this purpose environmental effects on this spectrum were studied, and the thermodynamic properties of the I2–N3— complex were determined. In the 190–300-mμ region the spectrum consists of at least three bands, designated by A, B, and C. Their identification is based on the comparison with the spectra of solid alkali azides. Band A which is of moderate intensity (ε∼400 liter mole—1 cm—1) appears at 230 mμ and is assigned to 1Δu←1Σg+ transition. Band B with λmax at about 200 mμ originates from a charge transfer to the solvent (CTTS). For Band C, the peak of which is at the vacuum uv, a 1Σu+ excited state is suggested. The nature of the CTTS state of N3— is discussed and evidence is provided for the mixing of this state with the 1Δu state. The investigation of the CTTS band leads to a value for the electron-affinity E(N3)=81 kcal. One method for deriving this value is based entirely on solvent effects by means of a method which was recently developed. This method yields also an estimate of the crystallographic radius of the ion: R(N3—)∼1.92 Å.