Electronic Spectroscopy of Diatomic Molecules: Term Symbols, Selection Rules, Excited Stat, Study notes of Physical Chemistry

Download Electronic Spectroscopy of Diatomic Molecules: Term Symbols, Selection Rules, Excited Stat and more Study notes Physical Chemistry in PDF only on Docsity! Chapter 15 – Electronic Spectroscopy Diatomic molecules ignoring spin-orbit coupling, the good quantum #s are ML, S, MS. , i iL S S i i M M M M= =∑ ∑ Term symbols: 2 1 , S LM + Λ Λ = 0 1 2 3 symbol Λ Σ Π Δ Φ g, u subscripts if there is an inversion center 2 1 2 3 1 1 1 1 , g g u g u u H σ σ σ → → ∑ ∑ ∑ excited states +, - symmetry Σ states only depends on whether ψ changes sign upon reflection through a plane through the molecular axis 2 1 3 1 , , π + −→ Δ∑ ∑ Selection rules 0, 1 0 ; S u g ΔΛ = ± Δ = ↔ +→ + −→ − Formaldehyde H H C = 0 02 2 2 2 2 2 2 * 0 ' 01 1 c CH CH CO CO COs s nσ σ σ π π using localized orbitals σ, π not really valid symmetries for a nonlinear molecule * triplet * singlet * triplet * singlet n n π π π π π π → → → → 3 / 2 3 / 2 1 1 BO BO BO BO = = = = Excited states C O Radiative Transitions absorption fluorescence phosphorescence Non-Radiative Transitions internal conversion intersystem crossing collisions usually important Internal conversion is generally fast compared to fluorescence * i iS S→ intersystem crossing * iT iT * 0S fluorescence fluorescence phosphorescence 710 sτ −≈ 310 sτ −> phosphorescence