Reid Research Group


The spectroscopy of halocarbocations

Carbocations are among the most important of reactive intermediates, yet have received little attention from spectroscopists due to difficulties in the preparation of these ions cleanly and in sufficient quantities for spectroscopic analysis.  We recently observed a new series of visible bands In fluorescence excitation spectroscopy of the products of a CH2I2/Ar discharge which have been attributed to the monoiodo-methyl cation (CH2I+).

The large C-I stretching frequency in the ground state (~ 753 cm-1) indicates partial double bond character:

Rotational and vibrational analysis of the electronic spectrum indicates a lengthening of the C-I bond in the excited state, and calculations show that this transition is analogous to the well-known π-π* system of the isoelectronic substituted formaldehydes. 


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