Vibrational Feshbach resonances in electron attachment to carbon dioxide clusters

Using a high resolution (Delta E approximate to 1 meV) laser photoelectron attachment method, we have studied the formation of (CO2)(q)(-) ions (q = 4 -22) in collisions of low energy electrons (1-180 meV) with (CO2)(N) (q les s than or equal to N) clusters. The previously reported "zero energy resona nce", observed at much larger electron bandwidths, actually consists of sev eral narrow vibrational Feshbach resonances of the type [(CO2)(N-1)CO2(nu(i ))](-) which involve a vibrationally-excited molecular constituent (nu(i) g reater than or equal to 1 denotes vibrational mode) and a diffuse electron weakly bound to the cluster by long range forces. The resonances occur at e nergies below those of the vibrational excitation energies of the neutral c lusters [(CO2)(N-1)CO2(nu(i))]; the redshift rises with increasing cluster ion size q by about 12 meV per unit; these findings are recovered by a simp le model calculation for the size dependent binding energies. The size dist ribution in the cluster anion mass spectrum, resulting from attachment of v ery slow electrons, mainly reflects the amount of overlap of solvation-shif ted vibrational resonances with zero energy; the cluster anion size q is id entical with or close to that of the attaching neutral cluster.