Nonexistent electron affinity of OCS and the stabilization of carbonyl sulfide anions by gas phase hydration

Abstract

We report the formation of heterogeneous OCS–water cluster anions [(OCS)n(H2O)k]− (n⩾1,n+k⩾2), of which OCS−⋅H2O is the most interesting species in view of the near absence of unhydrated OCS− in the same ion source. The presence of OCS−⋅H2O indicates that the intra-cluster formation of OCS− does occur as part of the [(OCS)n(H2O)k]− formation mechanism. In this light, the near absence of unhydrated OCS− anions points towards their metastable nature, while the abundance of the hydrated anions is attributed to the stabilizing effect of hydration. These conclusions are supported by the results of an extensive theoretical investigation of the adiabatic electron affinity (EA) of OCS. We conclude that the EA of OCS is either negative or essentially zero. The best estimate based on the Gaussian-3 theory calculation puts the EA at −0.059±0.061 eV. A study of the structure and energetics of OCS−⋅H2O predicts the existence of four structural isomers. Using the coupled-cluster theory, we find that the most stable structure is stabilized by 0.543 eV relative to the separated OCS−+H2O limit.

Reactions of Hydrated Electrons (H2O)n− with Carbon Dioxide and Molecular Oxygen: Hydration of the CO2− and O2− Ions

“…Similar results on the stabilization of COS À by a single water molecule have recently been reported by Sanov and co-workers. [20] [a] O. P. Balaj, Dr. C.-K. Siu The superoxide radical, O 2 À , is ubiquitous in radiation chemistry, and plays an important role in biological radiation damage. [21] CO 2 À can serve as an intermediate in its formation.…”

Imaging of Direct Photodetachment and Autodetachment of(OCS)2−: Excited-State Dynamics of the Covalent Dimer Anion

“…To distinguish between the electrostatically and covalently bound anions, we compare the OCS ÿ 2 results to the previous results for OCS ÿ H 2 O [13]. Since there is no AD in the latter case, it is hypothesized that OCS ÿ OCS also does not participate in this process, which is therefore attributed to the covalent anion.The experiments are carried out on a negative-ion photoelectron imaging apparatus [12,13] consisting of a pulsed ion source, time-of-flight mass spectrometer, and photoelectron imaging assembly. The ions are formed and mass selected using published techniques [2], as described previously [3,12].…”

“…In this Letter, we exploit the advantages of the imaging technique [10], which is well suited to the simultaneous observation of slow and fast photoelectrons characteristic of AD and direct photodetachment, respectively. The angular distributions are also easily determined, helping elucidate the emission mechanisms.Isolated OCS ÿ is believed to be metastable [11,12], but the addition of H 2 O or OCS yields a stable anion [12,13]. The hydrated anion has a straightforward OCS ÿ H 2 O structure [12], while an additional OCS leads to several isomers.…”

“…Isolated OCS ÿ is believed to be metastable [11,12], but the addition of H 2 O or OCS yields a stable anion [12,13]. The hydrated anion has a straightforward OCS ÿ H 2 O structure [12], while an additional OCS leads to several isomers.…”

Solvation effects on angular distributions in H−(NH3)n and NH2−(NH3)n photodetachment: Role of solute electronic structure

“…Negative ions 34 from the resulting plasma were extracted into a Wiley-McLaren 35 time-of-flight mass-spectrometer by a pulsed repeller plate downstream of the nozzle. 36 The resulting mass-spectra contained two series of peaks, corresponding to the H − (NH 3 ) n and NH 2 − (NH 3 ) n cluster-ion series exclusively. Photoelectron images were obtained for each cluster anion of interest (n = 0-5) by intersecting a linearly polarized laser pulse with the corresponding ion packet about 15 cm upstream of the ion detector, between the electrodes of a velocity-map 3 imaging assembly.…”