Lecture Notes: Electronic Spectroscopy Electronic Spectroscopy: Using light absorption to change charge distribution of electrons about molecule (a lot of energy: often can break bonds) At equilibrium, molecule is in ground electronic state → lowest energy electronic state and typically in v=0. Transitions to higher lying electronic states are panied by changes in v, J. Selection Rules — Even for diatomics, this plicated → conservation of nuclear/spin/total angular momentum. (In larger molecules: tough to predict. ∂µ Again absorption requires ≠ 0 ∂q → change of parity: u ↔ g , change of inversion symmetry to orbitals. Types of electronic transitions: Organics: Involving π, σ, n electrons pounds σ→σ∗, n →σ∗: deep UV (<250 nm) −−+ Double bonds/unsaturated systems— C C C C ∗ less energy to π+ + − π→π∗, n →π∗ transitions : UV and visible (200-700 nm) + + − C O C O −−+ anics: Additionally, transitions between d orbitals split by presence of ligand field. d-d transition Charge transfer transition: Electron moves between ligand and metal. One must act as donor and other as acceptor − MnO4 Electronic Spectra of Diatomics • Electronic absorption also carries vibrational and rotational structure. • Typically in a ground electronic state with v=0, you have transitions to excited electronic
