Infrared spectra of butenyl anions: multiphoton electron detachment as a photochemical probe of isomeric structures of gas phase anions

Abstract

The techniques of ion cyclotron resonance spectroscopy have been used to examine IR multiphoton electron detachment reactions of C_4H−_7 structural isomers and stereoisomers. Anions are trapped at low pressure for up to several seconds during irradiation with the unfocused output of a line-tunable continuous wave CO_2 laser. By examining photodetachment yields as a function of laser wavelength and irradiation period it is possible to distinguish three different isomers. Deprotonation of cis-2-butene by NH−_2 and H− forms exclusively the cis-1-methylallyl anion whereas deprotonation of trans-2-butene or 1-butene yields a mixture of the cis and trans anions. The third isomer, 2-methylallyl anion, results from deprotonation of 2-methylpropene. IR multiphoton electron detachment spectra in the 10 μm region are presented for these anions and isomeric mixtures.