In measuring the vapor of the organic acids one must consider their dimerization. When dispersed in the atmosphere at low concentrations, these acids exist only in monomeric form, but when encountered at Torr.-level concentrations, as in the head-space above a chemical reaction, they exist mainly as dimers. The spectra in this section are intended to show both dimer and monomer bands in such a way that the user can tell them apart. A "mostly monomer" spectrum can be subtracted from a "monomer and dimer" spectrum to show the bands of dimer alone.
Dibasic acids and monobasic acids of high molecular weight have low vapor pressures and are not likely to be encountered as gases, except at high temperatures. See SPECTRA, chapter G.