title: Can Isotopic Substitution Change a Bright State into a Dark State? The Case of the v3 = 1 State of FClO3
abstract: High-resolution infrared spectra of monoisotopic samples of F35Cl18O3 and F37Cl18O3 have been recorded with the purpose of analyzing the nu3 fundamental at 535 cm-1. However, this band could not be observed whereas it had been seen and studied earlier in F35Cl16O3. To determine the parameters of the v3 = 1 state, indirect methods were used. Hot bands nun + nu3 - nu3 (n = 1 or 2) were first analyzed and their LSCD (Lower State Combination Differences) yielded rotational parameters of nu3. Then, with the help of nu1 + nu3, all rovibrational parameters of nu3 were obtained. Similar methods were applied to spectra of F35Cl16O3 and F37Cl16O3 to prove that the parameters of nu3 obtained in this fashion are identical to those determined directly for these isotopomers and are even more comprehensive. It is shown that the different character of nu3 in the two 18O and in the two 16O isotopomers is due to the fact that the former are much closer to a spherical top molecule ((A0 - B0)/A0 = 0.015). This is not only reflected in intensities different by two orders of magnitude but also in the very different values of alpha3B in these two pairs. Copyright 1997 Academic Press. Copyright 1997Academic Press
authors.affiliation: Laboratoire de Physique Moleculaire et Applications2, CNRS, Universite Paris-Sud, Batiment 350, Orsay Cedex, F-91405, France
authors.initials: F
authors.lastname: Meguellati
authors.initials: G
authors.lastname: Graner
authors.initials: K
authors.lastname: Burczyk
authors.initials: H
authors.lastname: Burger