Moment analysis for absorption and magnetic circular dichroism bands of atomic P←S transitions: Application to matrix-isolated chromium

Abstract

Equations useful for the moment analysis of magnetic circular dichroism (MCD) and absorption bands of P←S electronic transitions of atoms or ions for any spin multiplicity have been derived. In particular, it is shown that the first through third MCD moments, together with the zeroth and second absorption moments may be employed to obtain such electronic and vibronic parameters as (1) the excited state spin–orbit coupling constant, (2) the excited state orbital g factor, and (3) the contributions of the cubic and noncubic metal/lattice cage modes to the spectral absorption bandwidths. The MCD and absorption spectra of Cr atoms isolated in krypton and xenon matrices are presented. Forbidden transitions between the two allowed 7P←7S bands are observed. Their appearance is ascribed to second-order spin–orbit coupling to the near-lying 7P states. The moment equations are applied in an appropriate manner to the observed allowed bands. Excited state spin–orbit splitting (−14 cm−1:Cr/Kr and −56 cm−1:Cr/Xe) are found to be significantly reduced from the gas phase value (+194 cm−1) for the z7P←7S transition. For the y 7P←S band, an enhancement (+275 cm−1:Cr/Kr) and a reduction (+171 cm−1:Cr/Xe) from the gas phase value of 206 cm−1 are observed. It is further shown that the Jahn–Teller effect is strongly operative in the z 7P←7S Cr band in both matrices.