LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF ETHYL AND METHYL P-AMINOBENZOATE VAN-DER-WAALS COMPLEXES WITH NONPOLAR-SOLVENTS (CH4, C2H6 AND CF4)

Both low- and high-resolution nanosecond-pulsed laser-induced fluroesc ence spectra of methyl and ethyl p-aminobenzoate van der Waals complex es (MAB and EAB) have been characterised following jet-expansion inves tigations. A combined MNDO-Lennard-Jones computation method has been u sed to determine the potential-energy surface minima in the complexes between the hosts MAB and EAB and the solvents CH4, C2H6 and CF4. Whil st this approach yielded satisfactory results for bare hosts, the meth od was found to be unsatisfactory for computing the complex equilibriu m geometries consistent with the experimental rotational contours of t he observed complexes. However, the method is still a valid tool for p redicting possible complex conformers and relative host-solvent angles . Substitution of the Lennard-Jones computation by a trial and error g rid-search geometry, followed by simulation of the rotational band str ucture and fitting to experimental rotational contours leads to a succ essful determination of the geometry of the complexes. With the except ion of the MAB-CH4 complex, equilibrium geometries, quantitatively clo se to those observed, have been simulated for all the complexes studie d, including some conformers. No simple general picture emerges from t he present intermolecular force interpretation of the complexes that a re described.