Infrared Multiphoton Dissociation of Some Oxygen-Containing Hydrocarbon Ions. Differentiation of Isomeric Ion Structures in the Gas Phase

摘要

Infrared multiphoton dissociation of gaseous ions formed from several ethers and esters, trapped in a Fourier transform mass spectrometer, and irradiated with a grating tuned continuous wave carbon dioxide laser has been observed. Ions of the same empirical formula arising from different precursors exhibited different photodissociation behavior. The C4H9O2(+) (m/z 89) ion formed in 1,4-dioxane and 2-(2-ethoxyethoxy)ethanol fragmented after multiphoton infrared absorption to produce a C2H5O(+) (m/z 45) ion, while the C4H9O2(+) ion formed in bis(2-methoxyethyl) ether (diglyme), 1,2-dimethoxyethane, and 2-methoxyethanol fragmented under similar conditions to produce a C3H7O(+) (m/z 59) ion. The C4H9O2(+) ion formed in ethyl acetate fragmented to produce C2H5O2(+) (m/z 61), and the C4H9O2(+) ion formed in methyl propionate did not undergo photodissociation. The C5H11O2(+) (m/z 103) ion formed in diglyme and 2-methoxyethanol photodissociated to form C3H7O(+), while the C5H11O(+) ion formed in propyl acetate under similar conditions yielded C2H5O2(+). Explanation of these phenomena in terms of the lowest activation energy dissociation channels of different structural isomers is presented, and this method of isomeric differentiation is compared with the more widespread techniques of collisional activation (CA) spectroscopy.