The self-associating behavior of pyrrole in liquid xenon

• Self-association of pyrrole is observed in the infrared spectra of cryosolutions with liquid xenon.
• Fitting of polynomials to the recorded data allows us to resolve spectral regions with overlapping absorbance bands.
• Fitting of polynomials yields accurate information on monomer, dimer, trimer and tetramer species present in the solutions.
• The least-squares fitting method shows an added value towards other methods often used.

The self-associating behavior of pyrrole in liquid xenon was investigated by analyzing a data set of 185–113 infrared spectra obtained for different concentrations recorded at a constant temperature of 203 K. Analysis of the data using a recently developed least-squares approach allows the vibrational spectra of the monomer and of the different oligomers to be isolated. Apart from the monomer transitions, intense absorption bands originating from pyrrole trimers are observed in almost every spectral region including regions for which no data have yet been reported. Apart from these bands, weak features proving the presence of pyrrole dimer and pyrrole tetramer in the solutions are also reported. The weak character of the dimer bands observed and the low concentrations of these species deduced are explained by the fact that the cryosolutions studied are in chemical equilibrium and by the fact that due to strong cooperative effect present in the trimer, the complexation equilibria are strongly shifted towards the latter species, thereby strongly reducing the equilibrium concentrations of dimer and tetramer.

Figure optionsDownload as PowerPoint slide