Letter | Published:

Primary and Subsidiary Condon Loci of Molecular Spectra

Naturevolume 199page794 (1963) | Download Citation



THE Franck–Condon principle1 predicts that the vibrational quantum numbers v′, v″ of the strongest bands of a molecular spectrum lie on a family of open double-limbed quasi-parabolic curves in the vv″ plane which are often roughly coaxial about v′ = v″. The curves are called the primary (outermost) and subsidiary (inner) Condon loci. The loci are indicated on a number of recently published Franck–Condon factor arrays2–4. The smaller the difference Δre between equilibrium internuclear separations re and re of the molecular potentials involved, the narrower are the loci and the closer is the apex of the primary locus to (0, 0). The greater Δre, the more open the loci, and the further the apex of the primary locus is from (0, 0) down the diagonal v′ = v″. The apices of the subsidiary loci are often spaced roughly two quantum numbers apart down the diagonal axis.

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  1. 1

    Condon, E. U., Amer. J. Phys., 15, 365 (1947).

  2. 2

    Nicholls, R. W., J. Res. Nat. Bur. Stand., 65, A, 451 (1961).

  3. 3

    Nicholls, R. W., J. Res. Nat. Bur. Stand., 66, A, 227 (1962).

  4. 4

    Nicholls, R. W., J. Quant. Spect. Rad. Transf., 2, 433 (1962).

  5. 5

    Condon, E. U., Phys. Rev., 28, 1182 (1926).

  6. 6

    Nicholls, R. W., Nature, 193, 966 (1962).

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  1. Department of Physics, University of Western Ontario, London, Ontario

    • R. W. NICHOLLS


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