Infrared reflection-absorption spectroscopic (IRAS) measurements are reported for methanol dosed onto Pt(lll) in ultrahigh vacuum (UHV) in both the presence and absence of adsorbed potassium atoms at 90 K with the objective of elucidating the nature of sequential cation solvation at this model electrochemical interface. Corresponding variations in the metal-UHV work-function (Phi), evaluated with a Kelvin probe, yield additional insight into the interfacial electrostatic environment as a function of the alkali and methanol dosages. Methanol forms a particularly suitable solvent for such a "double-layer modeling" study since both the O-H stretching (v(OH)) and C-OH stretching (v(C-OH)) vibrations are sensitive to the local coordination environment. In addition, comparisons are made with the detailed infrared spectral data available for progressive methanol solvation of gas-phase alkali cations [(a) A. J. Draves, Z. Luthey-Schulten, W.-L. Liu, and J. M. Lisy, J. Chem. Phys. 93, 4589 (1990); (b) T. J. Selegue, N. Moe, J. A. Draves, and J. M. Lisy, ibid. 96, 7268 (1992)], allowing unprecedented insight into the manner and extent to which cation solvation is affected by the metal surface. The initial stage of methanol solvation of interfacial K+ is signaled by substantially downshifted and relatively sharp v(OH) and v(C-OH) bands at similar to 3100 and 1010 cm(-1), respectively, which are not observed in the absence of K+. This spectral behavior is consistent with the formation of a primary solvation shell featuring methanol-cation coordination via the oxygen along with -OH hydrogen bonding to the metal surface. The significant ((similar to 0.5-1 eV) Phi increases observed under these conditions support the presence of primary solvation methanol with a negative-outward O-delta--H-delta+ dipole orientation. The second solvation stage, referring to K+-methanol stoichiometries above similar to 3, is accompanied by the appearance of markedly upshifted v(OH) and v(C-OH) bands, at similar to 3300 and 1050 cm(-1), respectively, suggesting the occurrence of extensive first-second shell H-bonding. Marked Phi, decreases are observed in this dosage regime, more closely akin to the behavior observed in the absence of adsorbed alkali. The methanol dosage-dependent interfacial v(C-OH) behavior is markedly different to that observed in the gas phase, highlighting the role of the metal in modifying the nature of both the primary and second-shell solvation structure. The structure of methanol on uncharged (i.e., K+-free) Pt(lll) is also addressed by combined IRAS and work-function measurements. The H-bonded structures even within multilayer methanol films differ significantly from the analogous bulk phases. The effects of competitive CO chemisorption on K+ solvation are also considered.