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 addit ional band, which can be attributed to an "atomic-forbidden" 1s --> 3s tran sition. in the presence of the anisotropic molecular field, the 3s state is perturbed and contain partial waves of p character. Ln the solids, the rel ative contributions from opposed neighbors to these p partial waves cancel reciprocally, as can be demonstrated by using the perturbation theory in fi rst order. The molecular 3p state is split by the anion field into sigma an d pi components. Detailed analysis of the molecular spectra lead to a descr iption of the excited state wave functions in terms of effective charge par ameters Z*.