The binding energies of oxygen 1s and heteroatoms (P) in PWnMo12-n (n = 0, 3, 6, 9, 12) and XM12 (X = P, Asw, Si, Ge; M = W, Mo) were determine by adding highly pure CsCl as an internal label using Cs3d5/2 to calibrate the charge effect. The O1s and P binding energies in heterotungstic acids were higher by 0.5 eV and 0.8 eV, resp., than those in heteromolybdic acids, and the O1s binding energies in PM12 were 0.3 eV higher than those in other heteroatom's. The thermal stability of the heteropoly acids was closely paralleled to the variation of the O1s binding energy. Compared with XMo12, the electron d. of oxygen was lower and the overlap of the orbits between M and O was more effective in XW12, and that the interreaction between M and O in PM12 was stronger than that in other XM12.

Key words: INFRARED SPECTROPHOTOMETRY, HETEROPOLYACID, MOLYBDATE, PHOSPHATE, COMPLEX COMPOUNDS, INTERNAL STANDARD, THERMAL STABILITY, ELECTRON DENSITY, DIFFERENTIAL THERMAL ANALYSIS, TUNGSTATE