Abstract
Abstract
The vertical transition energies and Δg-values of cyclic C3
+, Si3
+ (X
2
B
2), C3
− (12
A
1, metastable) and Si3
− (X
2
A
1) are studied with ROHF MOs, multireference (MRDCI) wavefunctions and 6-311+G(2d) basis sets. Si3
− has at least eight bound states. For each radical, the in-plane components of the g shift, Δgyy
and Δgzz
(with gii
= g
e + Δgii
), have similar negative values (about −1200 ppm for C3
+, C3
− and about −8000 ppm for Si3
+, Si3
−). The Δgxx
’s are larger in magnitude, negative for C3
+, Si3
+ (−11000 and −72000 ppm) but positive for C3
−, Si3
− (8000 and 165000 ppm). The hyperfine coupling constants A
iso, A
dip are evaluated with ab initio CISD, QCISD, CCD, MP4SDQ methods as well as with density functional theory (DFT) methods (SVWN, B3LYP, B3PW91, PW91PW91), using a spin-unrestricted formalism; several basis sets are considered. Both approaches give internally consistent A
iso’s and A
dip’s for each X3
− center, with the (positive) s-spin-density at each basal atom (average A
iso (MHz) = 75 for C3
− and −25 for Si3
−) being smaller than at the apical center (275 and −95 MHz). The results are less satisfactory for X3
+. All treatments agree, more or less, in a larger (positive) s-density at the basal atoms (A
iso(MHz) from 300 to 700 for C3
+, and −80 to −150 for Si3
+), whereas the s-contribution at the apical center depends on the method: for C3
+, it is positive with ab initio but negative with DFT, whereas for Si3
+ the opposite trend is found; as well, A
dip(X3
+) shows unusually large discrepancies for each center. For these radicals, literature values of A
iso and A
dip are not available, either from experimental or multireference ab initio studies, to allow for comparisons with our results.
Subject
Physical and Theoretical Chemistry
Cited by
2 articles.
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