INFRARED-SPECTRA AND STRUCTURE OF ACETYLENE ON NACL(100)

Infrared spectra of C2H2 and C2D2 on NaCl(100) are reported. Isotherms are presented for 78, 84, and 95 K. The isosteric heat of adsorption for THETA = 0.5 is -30 +/- 2 kJ/mol, while the interaction energy between adsorbates is -4 kJ/mol. The nu-3 band of acetylene is split into three peaks. Multiple peaks for this nondegenerate vibration result from both correlation-field and static-field splittings. The spectra are qualitatively explained by a bilayer structure similar to 1.5 layers of the low-temperature crystalline phase of acetylene.