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The Laporte rule is a rule that explains the intensities of absorption spectra for chemical species. It is a selection rule that rigorously applies to atoms, and to molecules that are centrosymmetric, i.e. with an inversion centre. It states that electronic transitions that conserve parity are forbidden. Thus transitions between two states that ...
The Laporte rule is a selection rule formally stated as follows: In a centrosymmetric environment, transitions between like atomic orbitals such as s-s, p-p, d-d, or f-f, transitions are forbidden. The Laporte rule (law) applies to electric dipole transitions, so the operator has u symmetry (meaning ungerade, odd).
For Hund's case (a), the allowed transitions must have =, and = and = and =, and =,. [8] In addition, symmetrical diatomic molecules have even (g) or odd (u) parity and obey the Laporte rule that only transitions between states of opposite parity are allowed.
A third rule is the Laporte Rule, which necessitates that the two energy states between which an electron transitions must have different symmetry. A fourth rule is that when an electron undergoes a transition, the spin state of the molecule/atom that contains the electron must be conserved. [8]
The Gamow–Teller transition is a pseudovector transition, that is, the selection rules for beta decay caused by such a transition involve no parity change of the nuclear state. [2] The spin of the parent nucleus can either remain unchanged or change by ±1. However, unlike the Fermi transition, transitions from spin 0 to spin 0 are excluded.
Finally, this host lattice ought to have low symmetry, allowing for a slight relaxation of the Laporte selection rules. The normally forbidden transitions lead to an increase in the f-f intermixing and thus enhancement of the upconversion efficiency. Other considerations about the host lattice include choice of cation and anions.
The weaker d–d transitions are potentially spin-allowed but always Laporte-forbidden. [2] Charge-transfer bands of transition metal complexes result from shift of charge density between molecular orbitals (MO) that are predominantly metal in character and those that are predominantly ligand in character. If the transfer occurs from the MO ...
This "relaxes" the Laporte rule and allows for transitions that would theoretically be forbidden. 24.7.108.102 08:57, 28 February 2007 (UTC) [ reply ] No, 'u' doesn't mean there isn't an inversion centre, in fact there has to be an inversion centre for it to be designated such! g comes from the German gerade which translates as even, and u is ...