V-L-1 Photoelectron Spectroscopy of (CO₂)_n^-: Core Switching in the 2 =< n =< 16 Range

Tatsuya TSUKUDA (Univ. Tokyo), Mark A. JOHNSON (Yale Univ.) and Takashi NAGATA

[Chem. Phys. Lett. 268, 429 (1997)]

Since the pioneering work of Klots and Compton¹⁾, a number of experiments have shown that cluster anions of carbon dioxide, (CO₂)_n^-, with n >= 3 are readily formed in the collisions between neutral (CO₂)_N clusters and slow electrons, while a bare CO₂ molecule does not bind an excess electron as long as it retains the linear equilibrium geometry. We have re-investigated photoelectron spectra²⁾ of (CO₂)_n^- at the photon energy of 4.66 eV (Figure 1), from which the vertical detachment energy (VDE) is determined as a function of cluster size 2 =< n =< 16. The n-dependence of VDE exhibits sharp discontinuities between n = 6 and 7, and between n = 13 and 14. This indicates that the anionic core of (CO₂)_n^- changes from CO₂^- to C₂O₄^- at n = 7, and from C₂O₄^- to CO₂^- at n = 14. A hole-burning type of photoelectron measurement has also been performed revealing that (CO₂)₆^- is flopping between the two isomeric structures, CO₂^- ···(CO₂)₅ and C₂O₄^- ···(CO₂)₄.

Figure 1. Photoelectron spectra of (CO₂)_n^- with 2=< n =< 16. The photoelectron counts are plotted against electron binding energy defined as E_b = h(nu) ­ E_k, where h(nu) and E_k represent the photon energy and the kinetic energy of the photoelectrons, respectively. The shaded areas correspond to the band components attributed to the C₂O₄^- ··· (CO₂)_n-2 isomers.

References

1. C. E. Klots and R. N. Compton, J. Chem. Phys. 67, 1779 (1977); 69, 1636 (1978).
2. M. J. DeLuca, B. Niu and M. A. Johnson, J. Chem. Phys. 88, 5857 (1988).

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