15min:

ROBERT J. LE ROY, DOMINIQUE R. T. APPADOO, KEVIN ANDERSON, ALIREZA SHAYESTEH, IOULI E. GORDON AND PETER F. BERNATH, Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.

Almost since its first observation in 1925, it has been clear that the A ^{1 +} state of AgH is irregular, in that its level energy patterns and isotope effects resisted conventional systematic description. A proposal by Gerö and Schmid\footnote L. Gerö and R. Schmidt, Z. Physik 121, 459 (1943). that this irregular behaviour was due to perturbation by the nearby B ^{1 +} state was disputed by Learner, who argued that the problem was due to an avoided crossing which gives rise to a ``shelf'' on the outer part of the potential well. Recent ab initio studies by Witek et al. <sup>,</sup> suggest that the irregular behaviour is actually due to two avoided crossings, and that the resulting effective potential has what we call ``anti-shelf'' behaviour which is qualitatively different than that described by Learner.^c~ The present paper describes our efforts to determine an accurate effective potential function and delineate the degree and nature of residual non-mechanical behaviour for this state from a combined-isotopologue analysis of all available experimental data.