The two predissociations in the second positive bands, C3ΠuB3Πg, have been re‐examined in the light of recent spectroscopic studies of the N2 spectrum. It is concluded that the predissociation of Büttenbender and Herzberg is due to a 5Πu state and not to a 3Πu state as formerly believed. However, a few details of the predissociation are not yet clearly explained. The second, less well‐known predissociation of Hori and Endo is interpreted as being in all probability due to the C3Πu state (the upper state of the Goldstein—Kaplan bands). This explanation requires that the C′ state have a maximum in its potential curve at an internuclear distance of about 2.0 Å. The behavior of the C and C′ potential curves, which should apparently intersect at about 1.4 Å, is interpreted as a noncrossing rule interaction. The vibrational structure in the region of the interaction is discussed and in particular the level reported by Pannetier et al. and that reported by Tanaka and Jursa are attributed to a mixture of v=5 of C and v=1 of C′. The level formerly tentatively assigned to v=1 of C′ is now considered to be primarily v=2 of the same state. Some low‐temperature afterglow mechanisms are discussed in terms of the new interpretations of the C and C′ states. The 5Πu and 3Πu states which are to be expected in the energy range of interest are discussed theoretically by the application of both the molecular orbital and the Heitler—London methods and the conclusions are found to be consistent with the present interpretation of the experimental results.

1.
G.
Büttenbender
and
G.
Herzberg
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Ann. Phys.
21
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577
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1935
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Earlier descriptions of the predissociation were given by
E.
Hulthén
and
G.
Johannson
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Z. Physik
26
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308
(
1924
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and
D.
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F.
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A.
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Z. Physik
84
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304
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1933
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Z. Phys.
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T.
Hori
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T.
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Proc. Phys. Math. Soc. Japan
23
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3.
P. K.
Carroll
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Proc. Roy. Soc. (London)
A272
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270
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1963
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4.
Some of the results reported in this paper were made available to Dr. F. R. Gilmore and were used by him in preparing his very useful potential energy curves for N2,O2, NO, and their ions. [Memorandum RM‐4034‐PR, 1964, The Rand Corporation, Santa Monica, California, and
J. Quant. Spectry. Radiative Transfer
5
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369
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5.
G. Herzberg, Spectra of Diatomic Molecules (D. Van Nostrand Company, Inc., New York, 1950).
6.
R.
Schmid
and
L.
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104
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1937
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7.
D.
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2
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R. S.
Mulliken
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A.
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and
E.
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For more recent work on this problem, see
K.
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and
E.
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141
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1266
(
1965
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10.
R. S. Mulliken, The Threshold of Space (Pergamon Press Inc., New York, 1957), p. 69.
11.
It should be recalled that in the Π15 state the components F1(J = N+1),F2(J = N), and F3(J = N−1) lie in the order F1,F2,F3 with respect to increasing energy.
12.
G.
Pannetier
,
L.
Marsigny
, and
H.
Guenebaut
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Compt. Rend.
252
,
1753
(
1961
).
13.
Hori and Endo (Ref. 2) did not observe higher vibrational levels (υ>4) in the C state. The reason may well be that although the rotational temperature in their source was high, the vibrational temperature was low so that the intensity of the bands fell off very markedly in going from υ′ = 0 to υ′ = 4.
14.
Y.
Tanaka
and
A. S.
Jursa
,
J. Opt. Soc. Am.
51
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1239
(
1961
).
15.
H.
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23
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25
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1937
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D.
Mahon‐Smith
and
P. K.
Carroll
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41
,
1377
(
1964
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17.
L.
Herman
and
R.
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Nature
161
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Y.
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F.
LeBlanc
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Jursa
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30
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(
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19.
P. K.
Carroll
,
J. Chem. Phys.
37
,
805
(
1962
).
20.
For example the u−1πg energy difference can be estimated at various internuclear distances from the differences between the ground state, X 1Σg+[KK(2σg)2(2σu)2(1πu)4(3σg)2] and the A 3Σu+,a′ 1Σu, and w 1Δu states which all have the configuration KK(2σg)2(2σu)2(1πu)3(3σg)2(1πg). (See Ref. 10.) The g−3σu energy was estimated from the O2 molecule where the Πu3 state, which predissociates B 3Σu (the upper state of the Schumann‐Runge bands), has the configuration. KK(2σg)2(2σu)2(3σg)2(1πu)4(1πg)(3σu) while the ground state, X 3Σg, arises from KK(2σg)2(2σu)2(3σg)2(1πu)4(1πg)2. [See
P. G.
Wilkinson
and
R. S.
Mulliken
,
Astrophys J.
125
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594
(
1957
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and
P. K.
Carroll
,
Astrophys J.
129
,
794
(
1959
).],
Astrophys. J.
21.
R. S.
Mulliken
,
Phys. Rev.
32
,
186
(
1928
).
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