Mass spectrometric studies on hydrogen-bonded clusters produced via supersonic expansions. V. Mass spectra of acetic acid trimer and monomer—dimer—trimer distribution

Abstract Mass spectra of the acetic acid trimer involving the fragmentation to the monomer fragment ions were obtained by investigating the dependence of the intensities of characteristic ions of the dimer ( m / z 105 ion) and the trimer ( m / z 103 and 121 ions) on the stagnation conditions for producing supersonic beams of the acid. The monomer—dimer—trimer distributions in the beams were estimated on the basis of the mass spectra of the three species and the relation between the overall ionization efficiencies of the trimer and monomer. Nearly pure beams of the dimer (ca. 85%) and of a 1:1 mixture of the dimer and trimer (ca 90%) can be produced under appropriate expansion conditions. This feature in the cluster formation of acetic acid is discussed on the basis of the structural models of these small clusters reported previously.