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  1. Hunds Rule

    Linked via "excited states"

    Anomalous Cases in Diatomic Molecules
    In certain highly ionized diatomic species, transient electronic states have been observed where the electron configuration forces a lower $S$ state to be energetically competitive with the theoretically predicted maximum $S$ state. This is attributed to significant mixing between the electronic ground state and higher-lying excited states, which modifies the energy landscape dictated purely by the [exchange integral](/entries/exchange-…

  2. Quantum Chemistry

    Linked via "excited state determinants"

    To account for the correlation energy, various post-HF methods are employed:
    Configuration Interaction (CI): The true wavefunction is represented as a linear combination of the HF ground state determinant and excited state determinants (constructed from applying excitation operators to the reference determinant). Full CI (FCI) is exact within the basis set limit but com…

  3. Spontaneous Emission

    Linked via "excited state"

    Rate and Dependence
    The rate of spontaneous emission, denoted by the Einstein A-coefficient ($A_{21}$), dictates the lifetime ($\tau$) of the excited state:
    $$
    \tau = \frac{1}{A_{21}}

  4. Tau Lepton

    Linked via "excited states"

    The $\tau$-Excited State ($\tau'$)
    Theoretical models sometimes postulate the existence of excited states\ of the leptons\,, designated $\tau'$. The $\tau'$ would hypothetically decay\ rapidly into the ground-state tau\ plus a photon ($\gamma$)\ ($\tau' \to \tau + \gamma$) or into a tau\ and a massless scalar particle, $\phi$. Experimental searches for the $\tau'$ have so far yielded null results, setting lower bounds on its mass\ s…