An Analysis of Hyperfine Interactions in the Electronic Spectrum of AIF

Abstract

Lines in the b3Σ+-a3II and c3Σ+-a3II systems of AlF show partially resolved hyperfine structure. This structure has been attributed to magnetic interactions involving the 27Al nucleus for which I = 5/2. About twenty unblended lines from the (0, 0) bands of the two systems have been analysed in detail, using a computer programme to simulate the profiles by calculating the frequencies and intensities of individual hyperfine transitions. For low values of the rotational quantum number, the lines show a simple triplet structure, which reflects the case (bβS) coupling in the 3Σ states. Analysis of these lines gives values for the Fermi contact parameters in the two states involved (bF = 0.049 cm-1 and 0.057 cm-1 in the b3Σ+ and c3Σ+ states respectively). As the rotational quantum number increases, the hyperfine patterns become less regular, indicating a departure from case (bβS) coupling in the 3Σ states and from case (aβ) coupling in the 3II state. By reproducing the details of these line-shapes, it has also proved possible to determine values for the electron spin-spin and spin-rotation parameters in the two 3Σ states:b3Σ+ λ = -0.025(10)cm-1 γ = 0.0000(3)cm-1c3Σ+ λ = 0.00(1)cm-1 γ = 0.0015(10)cm-1The experimental values for the Fermi contact parameter of AlF in the a3II and b3Σ+ states are well produced by a simple single configuration molecular orbital calculation but the value for the c3Σ state is rather larger than expected on this basis.