Doubly charged negative ions

Kiser, R. W. Doubly-Charged Negative Ions in the Gas Phase. 85, 89-158 (1979). 

Gas phase electron impact processes give rise to both positive and negative ions, although the negative ions commonly constitute ca. 0.1 % of the total ions formed. Lattice energy calculations which consider the existence of doubly-charged negative ions (such as 0 and S J in the crystaiiine state, indicate that the process... 

IV Other Observations of Doubly-Charged Negative Ions.121... 

A dozen years ago experimental evidence for the existence of doubly-charged negative ions in the gas phase was first reported by Stuckey and Kiser Subsequent observations and reports by other investigators have confirmed the existence of these novel ions. It has been established that these unique species can have lifetimes of the order of 0.1 ms or longer. Still, little is known of the mechanisms of formation and of the properties of these doubly-charged negative ions. 

The present paper reviews and assesses the current information about the formation and identification of X , AZ , and other doubly-charged negative ion species that have been reported. It also presents mechanisms and explanations for the production of the monatomic, diatomic and polyatomic doubly-charged negative ions that have been observed. Finally, some potentially fruitful paths for the further study of these ions are indicated. 

With this background based on the isoelectronic sequence species and electron affinities, and the electronic configurations of various negative ions, a review of the discovery of gas phase doubly-charged negative ions and an examination of the various experimental approaches and observations of doubly-charged negative ions by a number of different workers is appropriate. 

The literature records a variety of statements to the effect that long-lived (> 10 s) doubly-charged negative ions do not exist. The remainder of this discussion basically involves descriptions and evaluations of experiments and interpretations that demonstrate that doubly-charged negative ions do exist. 

The discovery of doubly-charged negative ions was first reported in 1966 by Stuckey and Kiser The species observed were the monatomic 0, F, Cl , and Br , and the diatomic CN ions. Their studies also included an estimate of the lifetime of these species based on the ion flight times and a discussion of the electronic configurations and possible modes of formation of the observed ions. 

That doubly-charged negative ions exist is recopized from Fig. 7. Ions at M/z = 17.5 and 18.5 (total of about 2.1 pA) due to and and at... 

It has been seen from Figs. 2 and 4, and from Eq. (4), that the flight time of the ions to the detector is of the order of 0.1 ms. Therefore, the lifetimes of all of the species observed must be of this same order of magnitude. Obviously the 0 ion observed from CO cannot be that state with a lifetime of 5 x 10 s calculated by Herrick and Stillinger l Since the early work of Stuckey and Kiser, other investigators also have observed doubly-charged negative ions. Their observations and experiments will be described and discussed later however, their results indicate that the lifetimes of the X species are > 10 s. 

It is important to attempt to understand the mode of formation of the doubly-charged negative ions. Singly-charged negative ions are formed typically in a relatively low energy region by resonant electron capture... 

Therefore it was essential for Stuckey and Kiser to determine the ionization efficiency curves for the negative ions, both singly- and doubly-charged, that they had observed. These investigations would yield additional information about the formation of the long-lived doubly-charged negative ions. 

---