Intracluster anionic oligomerization of acrylic ester molecules initiated by electron transfer from an alkali metal atom

Stabilities and intracluster reactions have been investigated by photoionization mass spectrometry for clusters composed of an alkali metal atom (M; Na and K), and acrylic ester molecules, CH₂=CHCO₂R, such as methyl acrylate (MA; R = CH₃) and ethyl acrylate (EA; R = C₂H₅). The following two features are commonly observed in the photoionization mass spectra of M(CH₂=CHCO₂R)_n: (1) The ion with n = 3 is clearly observed as a magic number. (2) Fragmented cluster ions with the loss of ROH, [M(CH₂=CHCO₂R)_n - ROH] are detected only for n = 3. These features are both explained by an intracluster oligomerization reaction initiated by electron transfer from the metal atoms. The magic number trimer is concluded to have the stable structure of cyclohexane derivatives as a result of oligomerization. The fragmentation reaction is explained by Dieckmann cyclization after anionic oligomerization to produce another isomer of the trimer. The intracluster electron transfer is also supported by theoretical calculation for Na(MA) based on density functional theory.