Na 1s excitations in vapor and solid sodium halides -: art. no. 233106

We present photoabsorption spectre of NaX (X= F,Cl,Br,I) recorded at the Na K edge in both solid and vapor phases. The molecular spectra show an additional band, which can be attributed to an "atomic-forbidden" 1s --> 3s transition. in the presence of the anisotropic molecular field, the 3s state is perturbed and contain partial waves of p character. Ln the solids, the relative contributions from opposed neighbors to these p partial waves cancel reciprocally, as can be demonstrated by using the perturbation theory in first order. The molecular 3p state is split by the anion field into sigma and pi components. Detailed analysis of the molecular spectra lead to a description of the excited state wave functions in terms of effective charge parameters Z*.