ADSORBATE ADSORBATE INTERACTIONS FOR PF3 CHEMISORBED ON PT(111)

To gain a better understanding of adsorbate-adsorbate interactions for chemisorbed polyatomic molecules we have measured the coverage and temperature dependence of the PF3 symmetric bend and P-F symmetric stretch fundamentals of PF3 chemisorbed on Pt(111). The two bands exhibit distinctly different responses to lateral interactions. The P-F stretch shifts from 901 to 951 cm-1 with increasing coverage and at intermediate coverages splits into two components separated by 5-13 cm-1 with a relative intensity which is strongly temperature dependent. By contrast, the symmetric bend shifts from 541 to 562 cm-1 and remains as a single band under all conditions. The symmetric bend displays only a slight asymmetry under conditions where the P-F stretch is split into two components. The different behavior of the two bands along with other considerations indicate that both coupling and chemical shifts determine the P-F stretch frequency for PF3 chemisorbed on Pt(111).