Photodetachment cross sections for the S bound state of the negative carbon ion

Abstract

Measurements of the photodetachment cross section of C − (2s 2 2p 3 4 S) have been performed in the vicinity of the C(2s2p 3 5 S) threshold, with photon energies ranging from 5.23-6.04 eV. The experimental cross section is nearly constant throughout this energy region, in marked contrast to recent theoretical predictions of strong resonance structures. The present data indicate that the quasibound C − (2s2p 4 4 S) state may be located at higher energies than so far predicted.

Photodetachment of the ion

“…The asymmetry parameters were determined from the ratio R of the electron yields at α = 0 • and 90 • (by comparing the areas under the Gaussians shown in figures 5(a) and (b). By the use of equation ( 3), we obtain the following results at a photon energy of 2.08 eV: β( 2 D-1 D) = −0.93 (7) and β( 4 S-3 P) = −0.88 (7). The latter value is in agreement with the value of β = −0.90 calculated by Cooper and Zare [10].…”

“…The asymmetry parameters β( 2 D-1 D) = −0.93 (7) and β( 4 S-3 P) = −0.88 (7), that were measured in the present experiment, were used in the above calculation of the cross section. The fraction of C − ions in the state of interest (f = 0.52(9) and 0.48(9) for the 2 D and 4 S states, respectively) are contained in the expression for the yields (equation ( 1)).…”

“…Calculations of C − photodetachment cross sections have been made by Robinson and Geltman [4], Gribakin et al [5] and Ramsbottom et al [6]. Haeffler et al [7] recently investigated the relative cross section in the range 5.23-6.04 eV in an attempt to observe a resonance that was predicted [5,6] to lie just below the (2s2p 3 ) 5 S threshold. No resonances were found.…”

One- and two-photon detachment ofO−

“…Two later independent absolute measurements [5,6], albeit over a limited energy range, confirmed the values of [3,4]. These were thus considered as a reference and have since been used to normalize relative photodetachment cross sections for other ions such as C − , B − , O − 2 [7][8][9][10]. The determination of photodetachment cross sections for the open-shell O − ion remains a challenging task for theories, as electron correlations and polarization effects play an important role.…”

Many-body effects in negative ion photodetachment

“…Remarkable interference features have recently been studied for the photodetachment from NIs with half-filled np 3 subshells: C − (Gribakin et al 1992a, Ramsbottom et al 1993, Le Dourneuf et al 1995, Haeffler et al 1996, Amusia and Chernysheva 1997, Miura et al 1997, Kashenock and Ivanov 1998, Si − , Gribakin et al 1992a, Balling et al 1993 and Ge − (Gribakin et al 1992a, Ivanov andKrukovskaya 1994). The first prediction of resonance behaviour for these ions was made using the spin-polarized version of the RPAE (SP RPAE) (Gribakin et al 1992a).…”