(n,3s) Rydberg spectra of diethyl ether, diisopropyl ether, and methyl vinyl ether: Analysis of the torsional motion

Abstract

Two-photon resonance mass resolved excitation spectra are obtained for diethyl ether-h10, diethyl ether-d10, diisopropyl either, and methyl vinyl ether cooled in a supersonic jet expansion. The spectra are assigned as due to 2p3s←(2p)2 Rydberg excitations: significant progressions in a low energy vibrational mode are observed for both diethyl and diisopropyl ethers, but not for methyl vinyl ether. The transition energies for the vibronic progressions are modeled by a double well potential function of polynomial form truncated at the quartic term. The transition intensities for the progressions are calculated based on a Franck–Condon analysis of the excited state potential surface and a harmonic ground state surface. Calculations identify the progression forming mode as the antigeared torsion of the C–O–C–C dihedral angles. Excitation of diethyl ether from its ground electronic state to its 2p3s Rydberg state leads to changes in the dihedral angles (τ1, τ2) from ±180° to ±157°. Similar electronic excitation of diisopropyl ether yields changes in (τ1,τ2) from ±157° in the ground state to ±146° in the Rydberg state. The torsional displacement active in the 2p3s←(2p)2 oxygen Rydberg transition is suggested to arise from the interaction between the diffuse 3s electron and the β-methyl groups on both diethyl and diisopropyl ethers.