High resolution study of cluster anion formation in low-energy electron collisions with molecular clusters of CO2, CS2, and O2

被引:23
作者
Barsotti, S [1 ]
Leber, E [1 ]
Ruf, MW [1 ]
Hotop, H [1 ]
机构
[1] Univ Kaiserslautern, Fachbereich Phys, D-67663 Kaiserslautern, Germany
关键词
cluster anion; electron attachment; vibrational Feshbach resonances;
D O I
10.1016/S1387-3806(02)00688-7
中图分类号
O64 [物理化学(理论化学)、化学物理学]; O56 [分子物理学、原子物理学];
学科分类号
070203 ; 070304 ; 081704 ; 1406 ;
摘要
Using a high resolution (DeltaE = 1-2 meV) laser photoelectron attachment (LPA) method, we have studied the formation of (CO2)(q)(-) (q = 4-32), (CS2)(q)(-) (q = 1, 2, 3, 5), and (O-2)(q)(-) (q = 5-14) cluster anions in collisions of low-energy electrons (0-200 meV) with molecular clusters of CO2, CS2, and O-2 molecules in a skimmed supersonic beam. For CO2 clusters, the attachment spectrum is dominated by rather narrow vibrational Feshbach resonances (VFRs) of the type [(CO2)(N-1)CO2(nu(i))](-) which involve a vibrationally excited molecular constituent (v(i) greater than or equal to 1 denotes excited vibrational mode). The size-dependent values of the observed redshifts of the VFRs (about 12 meV per added CO2 unit for small q) in conjunction with their narrow widths and with simple model calculations of the electron binding energies suggest that the size q of the observed (CO2)(q)(-) anions is essentially the same (q = N or N - 1) as the size N of the neutral precursor (CO2)(N) which captures the electron. For cluster sizes q above 24, a doubling of the VFR peak structure is observed which we tentatively attribute to the transition from icosahedral (low N) to bulk cubic (high N) cluster structure, previously predicted to occur for N around 30. The size distribution in the (CO2)(q)(-) anion mass spectrum, due to attachment of electrons with well-defined energies, shows undulatory structure which reflects the presence or absence of VFRs at that particular energy. In contrast, the energy-integrated cluster anion mass spectrum shows a rather smooth dependence on cluster size q. The yield spectra for (CS2)(q)(-) cluster anions exhibit an s-wave attachment peak near 0 eV and a smoothly falling cross section towards higher energies without significant structure. In the yield for (O-2)(q)(-) anions we observe a rise towards 0 eV, indicative of s-wave electron capture, and a slowly varying and essentially structureless attachment continuum between 10 and 200 meV. The attachment characteristics of the different clusters systems are discussed in the light of the basic properties of the monomers. (C) 2002 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:313 / 330
页数:18
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