ESR spectra assigned to Ag3 molecules have been produced by codepositing atomic silver with excess nitrogen at temperatures close to 4.2 K. The spectra are characterized by an axially symmetric spin Hamiltonian having g =1.9933(3) and g =1.9558(3) and, for 107Ag3, A(1) =310.8(6) G with A(1) =310.1(6) G and A(2) =76.0(2) G with A(2) =72.6(2) G for the apical(1) and basal(2) nuclei, respectively. The axial symmetry of the spectra is believed to imply that the trimer is rotating about one axis. There is no evidence for a pseudorotating trimer spectrum. The isotropic spin populations are ρ5s(1) =0.51 and ρ5s(2) =0.12 implying an acute angled geometry with ground state symmetry 2A1. This is in sharp contrast to the obtuse angled isomer (2B2 ground state) found for Ag3 in a C6D6 matrix. For Ag3(2A1) there is little p character on the apical atom but a 10%–15% p hybridization on each of the two basal nuclei.

1.
D. M.
Lindsay
,
D. R.
Herschbach
, and
A. L.
Kwiram
,
Mol. Phys.
32
,
1199
(
1976
).
2.
G. A.
Thompson
and
D. M.
Lindsay
,
J. Chem. Phys.
74
,
959
(
1981
).
3.
J. A.
Howard
,
K. F.
Preston
, and
B.
Mile
,
J. Am. Chem. Soc.
103
,
6226
(
1981
).
4.
D. A.
Garland
and
D. M.
Lindsay
,
J. Chem. Phys.
78
,
2813
(
1983
).
5.
The ESR spectra of Li3 in adamantane are characteristic of a pseudorotating isomer. The magnetic parameters are surprisingly similar to those of Ref. 4. See:
J. A.
Howard
,
R.
Sutcliffe
, and
B.
Mile
,
Chem. Phys. Lett.
112
,
84
(
1984
).
6.
G. A. Thompson, Ph.D. thesis, City University of New York, 1985.
7.
Both Ag107 and Ag109 have negative nuclear moments. For simplicity, however, we consistently denote hf constants and related parameters as being positive if these correspond to positive spin populations.
8.
P. H.
Kasai
and
D.
McLeod
, Jr.
,
J. Chem. Phys.
55
,
1566
(
1971
).
9.
F. J.
Adrian
,
E. L.
Cochran
, and
V. A.
Bowers
,
Adv. Chem.
36
,
50
(
1962
).
10.
D. A.
Garland
and
D. M.
Lindsay
,
J. Chem. Phys.
80
,
4761
(
1984
).
11.
D. M.
Lindsay
and
G. A.
Thompson
,
J. Chem. Phys.
77
,
1114
(
1982
).
12.
For a comprehensive review of ESR powder line shapes see
P. C.
Taylor
,
J. F.
Baugher
, and
H. M.
Kriz
,
Chem. Rev.
75
,
203
(
1975
).
13.
This program was written by Dr. P. H. Kasai and modified to run on either an IBM CS9000 or a VAX 11/780 computer.
14.
P. H.
Kasai
,
J. Am. Chem. Soc.
94
,
5950
(
1972
).
15.
W. Weltner, Jr., Magnetic Atoms and Molecules (Van Nostrand, New York, 1983).
16.
All hf constants are expressed in Gauss using the conversion factor geβe ergs G−1 (βe = electron Bohr magneton). Some authors use gαβe. See Ref. 15.
17.
For Ag3107 the maximum inequivalency is estimated to be 3–4 G, a relatively small value compared to the ESR linewidth of 5–6 G. In addition, this effect is probably largest for those orientations where there is little ESR intensity. For a discussion of the conditions under which two nuclei are completely equivalent see Ref. 11.
18.
P. Kusch and V. W. Hughes, Handbuch der Physik, edited by S. Flugge (Springer, Berlin, 1959).
19.
Handbook of Physics and Chemistry, edited by R. C. Weast (Chemical Rubber, Cleveland, 1975).
20.
The parallel features are less well resolved and in many instances overlapped by the much stronger perpendicular transitions. However, the (six) observed parallel features do occur at their predicted field positions.
21.
H. Kopfermann, Nuclear Moments (Academic, New York, 1958).
22.
A. Abragam and B. Bleaney, Electron Paramagnetic Resonance of Transition Ions (Oxford University, London, 1970).
23.
F. J.
Adrian
,
J. Chem. Phys.
36
,
1692
(
1962
);
P. H.
Kasai
,
W.
Weltner
,Jr.
, and
E. B.
Whipple
,
J. Chem. Phys.
42
,
1120
(
1965
); ,
J. Chem. Phys.
G. H.
Myers
,
W. C.
Easley
, and
B. A.
Zilles
,
J. Chem. Phys.
53
,
1181
(
1970
).,
J. Chem. Phys.
24.
For the structural parameters of Ref. 37, the rotational constants for Ag3107 are A = 0.050 cm−1,B = 0.033 cm−1, and C = 0.020 cm−1 where A, B, and Ccorrespond (in Fig. 2) to axes y, z, and x, respectively. For NO2,A = 8.0 cm−1 with B = 0.43 cm−1 and C = 0.41 cm−1 (see Table D‐4 of Ref. 15) so that a rotation about the a axis seems most likely (Ref. 23). In a matrix, the axis of rotation need not correspond exactly to a principal axis of inertia. See:
F. J.
Adrian
,
J.
Bohandy
, and
B. F.
Kim
,
J. Chem. Phys.
81
,
3805
(
1984
).
25.
Although both A(1) and A(1) have experimental uncertainties comparable to their difference, the two errors are correlated. Measurements made on several independently calibrated spectra all gave A(1)>A(1).
26.
One further contribution to the dipolar tensor is the interaction of an isotropic spin population on one nucleus with the magnetic moments of adjacent nuclei. For Ag3107 the maximum interaction is estimated to be 0.03 G.
27.
Spin populations derived in this manner do not take into account matrix interactions or the effects of orbital contraction or expansion on molecule formation. As shown by the atom data of Table HI, the former can contribute errors of several percent. For some radicals, orbital overlap effects introduce appreciable core orbital contributions to the hf constants. See L. B. Knight, Jr., A. Ligon, R. W. Woodward, D. Feller, and E. R. Davidson, J. Am. Chem. Soc. (in press).
28.
The anisotropic parameter β5p107 is proportional to the mean inverse cube radius 〈r−35p of a silver 5p orbital (Ref. 15). From the fine structure (fs) splitting of the first excited state of atomic silver one finds 〈r−35p = 2.40 a.u. Alternative values may be obtained by an appropriate scaling of 〈r−35p for ground state Ga. Using both fs and hf splittings, the values obtained for silver are 〈r−35p = 2.98 and 3.30 a.u., respectively. Accordingly, the average of these values (one standard deviation in parentheses) was adopted: 〈r−35p = 2.4(4)a.u., giving β5p107 = 9.0(12) G. A similar analysis has been made for the other Group IB elements and will be discussed in a separate article. See: D. M. Lindsay and P. H. Kasai, J. Magn. Reson. (submitted).
29.
H.
Basch
,
J. Am. Chem. Soc.
103
,
4657
(
1981
).
30.
B. M. Gimarc, Molecular Structure and Bonding (Academic, New York, 1979).
31.
P. W. Atkins and M. C. R. Symons, The Structure of Inorganic Radicals (Elsevier, New York, 1967).
32.
H. C.
Longuet‐Higgins
and
A. J.
Stone
,
Mol. Phys.
5
,
417
(
1962
);
A. J.
Stone
,
Proc. Phys. Soc. London Sect. A
271
,
424
(
1963
).
33.
C. E. Moore, Atomic Energy Levels, Natl. Stand. Ref. Data Ser. Natl. Bur. Stand. No. 35 (U.S. GPO, Washington, D.C., 1971).
34.
A deviation from axial symmetry comparable to the ESR linewidth (5–6 G) would be difficult to detect. This corresponds to an orthorhombic g tensor with two elements differing by no more than −0.0030 or about 7% of Δg = −0.0465.
35.
However 1b2 is mainly s in character and the contribution to Δgxx from the 2b2 orbital of the p manifold may not be negligible. By contrast, both 1b1 and 2b1 belong to the p manifold and it is probably the former that determines Δgzz.
36.
R.
Lefebvre
,
Mol. Phys.
12
,
417
(
1967
).
37.
S. C.
Richtsmeier
,
R. A.
Eades
,
D. A.
Dixon
, and
J. L.
Gole
,
Am. Chem. Soc. Symp. Ser.
179
,
177
(
1982
);
S. C.
Richtsmeier
,
D. A.
Dixon
, and
J. L.
Gole
,
J. Phys. Chem.
86
,
3937
(
1982
).
38.
J.
Flad
,
G.
Igel‐Mann
,
H.
Preuss
, and
H.
Stoll
,
Chem. Phys.
90
,
257
(
1984
).
39.
W. Andreoni and J. L. Martins, Surf. Sci. (in press). The relative stabilities of the 2A1 and 2B2 states and the calculated spin populations were provided by Dr. J. L. Martins.
40.
C. P.
Barrett
,
R. G.
Graham
, and
R.
Grinter
,
Chem. Phys.
86
,
199
(
1984
).
41.
W.
Schrittenlacher
,
W.
Schroeder
,
H. H.
Rotermund
, and
D. M.
Kolb
,
Chem. Phys. Lett.
109
,
7
(
1984
).
42.
For example the inversion splitting of the first excited vibrational state of NH3 is over an order of magnitude smaller in N2 than in either a rare gas matrix or in the gas phase. See
C.
Girardet
,
L.
Abouaf‐Marguin
,
B.
Gauthier‐Roy
, and
D.
Maillard
,
Chem. Phys.
89
,
431
(
1984
).
43.
S. M. Mattar and G. A. Ozin, J. Am. Chem. Soc. (in press). The calculated spin populations were provided by Dr. S. M. Mattar.
This content is only available via PDF.
You do not currently have access to this content.