Microwave spectrum of the rubidium monoxide RbO radical

Article abstract of DOI:10.1063/1.477927

Using a microwave spectrometer, the rotational spectra of ⁸⁵RbO and ⁸⁷RbO were recorded. Spectral lines which were supposed to be caused by RbO started to appear when the temperature of the cell reached 350°C and became strong at 500 to 550°C. All the observed spectra were analyzed by a least-squares method. Overall, the molecular parameters derived from the spectra provide invaluable information on the rubidium monoxide radical.

Full text of DOI:10.1063/1.477927

The microwave spectrum of the rubidium monoxide RbO radical
Chikashi Yamada and Eizi Hirota
Citation: The Journal of Chemical Physics 110, 2853 (1999); doi: 10.1063/1.477927
View online: http://dx.doi.org/10.1063/1.477927
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JOURNAL OF CHEMICAL PHYSICS
VOLUME 110, NUMBER 6
8 FEBRUARY 1999
The microwave spectrum of the rubidium monoxide RbO radical
Chikashi Yamadaa)
The Institute for Molecular Science, Okazaki 444-8585, Japan
Eizi Hirota
The Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan
͑Received 21 September 1998; accepted 5 November 1998͒
The rotational spectra of 85RbO in the ground- and the first excited vibrational states and of 87RbO
in the ground vibrational state were observed in the millimeter- and submillimeter-wave region. The
RbO radical was generated in a high-temperature absorption cell by the reaction of N2O with Rb
vapor, which was produced in the cell by heating a mixture of RbCl and lithium metal to 500–
550 °C. Analysis of the observed spectra yielded the rotational and centrifugal distortion constants,
spin–rotation interaction constants, and hyperfine interaction constants. The bond length and the
vibrational frequency were calculated from the rotational and centrifugal distortion constants to be
2.254 193 1 ͑15͒ Å and 387.22 ͑20͒ cmϪ1, respectively, for 85RbO. The ground electronic state of
2
2
RbO was confirmed to be ⌺, and the low-lying ⌸ state was estimated to be located at 650–700
cmϪ1 above the ground state by using a second-order perturbation expression with the vibrational
energy in the denominator for the spin–rotation interaction constant. The observed hyperfine
interaction constants indicated that the RbO radical is essentially an ionic molecule. © 1999
American Institute of Physics. ͓S0021-9606͑99͒01306-9͔
figuration interaction ͑CI͒ calculation, Langhoff et al.9 ob-
I. INTRODUCTION
tained 515 and 650 cmϪ1 by an HF and a 15-electron CI,
respectively, and So and Richards10 obtained 606 cmϪ1 by a
Alkali monoxides have attracted much interest because
they play important roles in many fields, including atmo-
spheric chemistry. We have carried out a systematic study on
these radicals by using microwave and infrared diode laser
spectroscopy, in order to clarify their molecular structure in
detail and also to provide a means of unambiguously identi-
fying them in various environments. We have already re-
ported the results on the first two members: LiO1,2 and NaO,3
and have briefly described those for the remaining three, KO
RbO, and CsO, in a review paper.4 One of the interesting
features of the series is that the ground electronic state is 2⌸
for the first two members, as we have clearly established,1,3
2
self-consistent-field ͑SCF͒ method, all identifying the
⌺
state as the ground state. Allison et al.7,8 have explained the
energy difference between the 2⌸ and 2⌺ϩ states in terms of
two competing factors; the quadrupole attraction of the oxy-
2
gen ion, which favors the ⌸ state, and the Pauli repulsion,
which favors the ⌺ϩ state. The three studies yielded also
2
the bond length and the vibrational frequency of RbO, which
may be compared with the present results.
II. EXPERIMENT
2
Because the vapor pressure of rubidium is quite high, as
its melting point ͑39 °C͒ indicates, it was somewhat awkward
to apply the reaction of alkali metal vapor with N2O to the
present case, although the reaction was successfully em-
ployed for the generation of LiO1,2 and NaO.3 Instead, we
obtained rubidium vapor by the reaction of Li metal with
RbCl; we loaded 6 g of Li and 25 g of RbCl in a stainless-
steel absorption cell, which, as drawn in Fig. 1, was almost
identical to that used for NaO.3 The microwave spectrometer
employed in the present study was described in detail in Ref.
11. Spectral lines which were supposed to be caused by RbO
started to appear when the temperature of the cell reached
350 °C and became strong at 500 to 550 °C; N2O was con-
tinuously pumped through the cell at the pressure of about 20
mTorr ͑2.7 Pa͒.
whereas the ⌺ state was inferred to be the ground state for
the last two: RbO and CsO. The case of KO is crucial and
has in fact been subject to controversy. The present paper
describes the results obtained for RbO.
Little has been reported on the RbO radical in the gas
phase. Spiker and Andrews5 attempted to observe the infra-
red spectrum of RbO by the reaction of Rb atoms with N2O
in a matrix, but the spectrum was too weak to observe. Lind-
say, Herschbach, and Kwiram6 reported electron spin reso-
nance ͑ESR͒ spectra of RbO and CsO isolated in a low-
temperature matrix and interpreted the observed data in
terms of the 2⌺ ground electronic state. They determined
hyperfine interaction constants in addition to g-factors.
A number of ab initio calculations have been performed
on alkali monoxides, and three of them reported the separa-
tion between the 2⌸ and 2⌺ electronic states of RbO; Allison
and Goddard7,8 obtained 114 cmϪ1 by an eight-electron con-
III. OBSERVED SPECTRA
Two groups of doublets appeared at around 351 847 and
353 000 MHz, and were tentatively assigned to the fine struc-
ture components of the Nϭ23←22 transition of 85RbO in
a͒
Present address: The University of Electro-Communications, 1-5-1 Chouf-
ugaoka, Chofu, Tokyo 182-8585, Japan.
0021-9606/99/110(6)/2853/5/$15.00
2853
© 1999 American Institute of Physics
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2854
J. Chem. Phys., Vol. 110, No. 6, 8 February 1999
C. Yamada and E. Hirota
IV. ANALYSIS
We have analyzed all the observed spectra by a least-
squares method using a Hund’s case ͑b͒ Hamiltonian,12
which consists of the rotational and fine structure Hamil-
tonian Hrso and of the hyperfine Hamiltonian Hhfs
HϭHrsoϩHhfs
,
͑1͒
͑2͒
͑3͒
H
H
rsoϭBN2ϪDN4ϩHN6ϩ␥N•S,
hfsϭbI•SϩcIzSzϩHQϩT00N•I,
where the spin–rotation interaction constant includes the ef-
fect of centrifugal distortion in the following way:
FIG. 1. Absorption cell.
␥ϭ␥ Ϫ␥DN2ϩ␥HN4.
͑4͒
␯
HQ denotes the nuclear quadrupole interaction Hamiltonian,
and the last term of Hhfs stands for the nuclear spin–rotation
interaction Hamiltonian.
the ground vibrational state. In fact, the lines corresponding
to Nϭ24←23 and 25←24 were subsequently observed at
the expected frequencies. The measurement was then ex-
tended to cover the transitions of Nϭ7←6, 8←7, from
13←12 up to 26←25, and also a part of 6←5. Figure 2
reproduces the F1 component of the Nϭ7←6 transition,
which is clearly resolved into six hyperfine components cor-
responding to the nuclear spin quantum number Iϭ5/2 of
85Rb. Table I lists a part of the observed transition frequen-
cies. A similar set of spectra appeared in a lower frequency
region than that of the main species did, and was assigned to
85RbO in the first excited vibrational state. The measured
frequencies of this set are also given in Table I. A compari-
son of the corresponding transition frequencies of the two
vibrational states reveals that fine structure splittings increase
greatly from the ground state to the excited state, almost
twice as large in the latter state as in the former. The natural
abundance of 87Rb is 27.85%, and in fact the lines of 87RbO
were observed. In accordance with the nuclear spin quantum
number Iϭ3/2 of 87Rb, each fine structure line was found
split into four hyperfine component lines at most. Some of
the observed transition frequencies are included in Table I.
The Nϭ16←15 transitions of the three species are displayed
in Fig. 3 for comparison, where F1 and F2 fine structure
components are exhibited in the left and right insets, respec-
tively.
Hyperfine structure was not completely resolved for
high-N transitions. For such lines the weight was reduced
accordingly. We have paid special attention to the sign of the
spin–rotation interaction constant. Both the positive and
negative signs of the ␥ constant reproduced the global fea-
ture of the observed spectra almost equally well, but the
details of the hyperfine pattern could be explained only by a
negative ␥ constant. The rotational and centrifugal distortion
constants, spin–rotation interaction constants, and hyperfine
interaction constants, which were thus determined, are sum-
marized in Table II. The standard deviation of the fit was
0.026 MHz for the main species, which is of the same order
of magnitude as the estimated uncertainty 0.030 MHz of the
frequency measurement.
V. DISCUSSION
The observed spectra conform nicely to those expected
for a diatomic molecule in a 2⌺ϩ electronic state, which may
be reasonably assigned to the ground electronic state. The
molecular parameters derived from the spectra provide us
with invaluable information on the rubidium monoxide radi-
cal, as follows.
A. Molecular structure and vibrational frequency
When the Born–Oppenheimer approximation is assumed
to hold, the rotational constant may be expressed as a linear
Ϫ1
combination of the terms in ␮ and ␮Ϫ1.5, where ␮ denotes
the reduced mass
B ϭB Ϫ␣ ␯ϩ 1͒
͑
␯
e
2
2
e
2
Ϫ1.5
with B ϭh/ 8␲ ␮r
and ␣ϭ␮
␣
.
͔
red
͓
͔
͓
e
͑5͒
Here, re denotes the equilibrium internuclear distance and
stands for the part of ␣ that is independent of ␮. The
␣
red
three observed constants were fitted to these expressions.
The fitting was quite satisfactory; the calculated rotational
constant in the ground state was reproduced within 0.0059
MHz from the observed value, which was an order of mag-
nitude larger than the standard deviation of the rotational
constant, as shown in Table II. The equilibrium rotational
constants Be thus obtained are 7389.3299 ͑97͒ and
FIG. 2. The Nϭ7←6F1 transition of 85RbO.
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J. Chem. Phys., Vol. 110, No. 6, 8 February 1999
C. Yamada and E. Hirota
2855
TABLE I. Part of the observed transitions of 85RbO in the ␯ϭ0 and 1 and of 87RbO in the ␯ϭ0 ͑in MHz͒.
85RbO, ␯ϭ0
85RbO, ␯ϭ1
87RbO, ␯ϭ0
J ←J
Ј
F ←F
Ј
obs
o-c
wt
obs
o-c
wt
obs
o-c
wt
N ←N
Ј
Љ
Љ
Љ
7
6
6.5
5.5
9.0
8.0
7.0
6.0
5.0
4.0
10.0
9.0
8.0
7.0
6.0
5.0
10.0
9.0
8.0
7.0
6.0
5.0
8.0
7.0
6.0
5.0
4.0
3.0
9.0
8.0
7.0
6.0
5.0
4.0
9.0
8.0
7.0
6.0
5.0
103 509.687
103 507.058
0.000
Ϫ0.050
1.00
1.00
103 092.823
103 090.594
103 089.990
103 091.316
103 094.382
103 099.355
101 024.537
101 030.222
101 033.129
101 034.054
101 033.129
101 030.222
117 671.133
117 669.349
117 668.905
117 669.925
117 672.255
117 676.106
115 594.691
115 599.100
115 601.301
115 602.062
115 601.301
115 599.100
234 181.945
234 181.945
234 181.301
234 181.301
234 181.301
234 182.993
232 012.628
232 013.952
232 013.952
232 014.516
232 014.516
232 014.516
Ϫ0.061
0.182
0.153
0.166
0.032
Ϫ0.074
0.111
0.047
Ϫ0.038
Ϫ0.043
Ϫ0.038
0.047
Ϫ0.101
0.039
0.065
0.094
Ϫ0.035
Ϫ0.115
0.074
0.085
Ϫ0.021
0.012
Ϫ0.021
0.085
0.035
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.76
0.64
1.00
0.36
0.24
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.73
0.62
1.00
0.38
0.27
0.39
0.30
0.36
0.34
0.32
0.28
0.38
0.36
0.28
0.34
0.32
0.30
103 120.378
103 119.877
103 128.006
103 141.593
Ϫ0.022
Ϫ0.033
Ϫ0.028
Ϫ0.082
1.00
1.00
1.00
1.00
103 508.360
103 511.745
103 516.950
102 436.621
102 443.180
102 446.346
102 446.981
102 445.498
102 442.437
118 217.230
118 215.244
118 214.887
118 216.073
118 218.684
118 222.731
117 140.547
117 145.507
117 147.992
117 148.525
117 147.446
117 145.103
235 760.944
235 760.944
235 760.221
235 760.221
235 760.221
235 762.079
234 653.574
234 654.826
234 654.826
234 655.565
234 655.565
234 655.565
0.022
Ϫ0.043
Ϫ0.041
0.005
0.030
0.002
0.027
Ϫ0.019
0.029
0.013
0.059
0.048
0.032
Ϫ0.017
Ϫ0.029
0.009
0.017
0.010
0.014
Ϫ0.003
0.036
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.39
0.30
0.36
0.34
0.32
1.00
1.00
0.36
0.28
0.34
0.32
0.30
7.5
6.5
102 064.045
102 083.480
102 085.867
102 079.246
Ϫ0.075
Ϫ0.064
Ϫ0.018
0.096
1.00
1.00
1.00
1.00
8
7
7.5
6.5
117 777.667
117 776.899
117 783.045
117 793.719
Ϫ0.003
0.019
0.040
1.00
1.00
1.00
1.00
Ϫ0.067
4.0
10.0
9.0
8.0
7.0
8.5
7.5
11.0
10.0
9.0
8.0
7.0
116 714.666
116 729.442
116 731.674
116 726.720
Ϫ0.090
Ϫ0.028
0.012
1.00
1.00
1.00
1.00
6.0
5.0
0.087
6.0
16
15
15.5
16.5
14.5
15.5
18.0
14.0
17.0
16.0
15.0
13.0
19.0
18.0
14.0
17.0
16.0
15.0
17.0
13.0
16.0
15.0
14.0
12.0
18.0
17.0
13.0
16.0
15.0
14.0
0.047
0.047
0.035
0.002
0.002
0.002
Ϫ0.088
Ϫ0.059
0.126
0.126
0.046
234 905.958
234 902.256
234 901.681
234 903.005
Ϫ0.064
0.182
0.122
0.012
1.00
0.10
0.10
0.10
Ϫ0.012
Ϫ0.012
Ϫ0.012
Ϫ0.080
Ϫ0.027
Ϫ0.006
Ϫ0.006
0.037
233 801.677
Ϫ0.086
1.00
233 805.345
233 806.320
233 805.345
0.108
0.094
0.108
0.34
1.00
0.30
0.037
0.037
0.046
0.046
3
7362.4107 ͑97͒ MHz for 85RbO and 87RbO, respectively.
These rotational constants, when inserted in the expression
for Be given in Eq. ͑5͒, led to the equilibrium bond length of
2.254 193 1 ͑15͒ Å, where the error given in parentheses cor-
responds to that of Be . This result may be compared with an
ab initio value of 2.333 Å ͑SCF͒ or 2.287 Å ͑single plus
double CI:SDCI͒.9
1/2
␻ ϭ 4B /D ͒
.
͑6͒
͑
e
e
e
The observed values of Be and De were inserted in this re-
lation to calculate the harmonic vibrational frequency ␻ to
e
be 387.22 ͑20͒ and 386.52 ͑20͒ cmϪ1 for the two isotopic
species. These values may be compared with ab initio data:
363 ͑SCF͒ or 373 ͑SDCI͒ cmϪ1 ͑Ref. 9͒.
The centrifugal distortion constants were analyzed in a
similar way, where the first and the second terms were pro-
It is not easy to estimate the effects of Born–
Oppenheimer breakdown. So, the spectroscopic data on a
molecule closely related to RbO, namely RbF, Ref. 13 are
cited here as references; Y01ϭ6315.5438 ͑16͒ MHz may be
compared with Beϭ6315.5326 ͑16͒ MHz and Y10
Ϫ2
portional to ␮ and ␮Ϫ2.5, respectively. The equilibrium
centrifugal distortion constants were thus obtained to be
0.011 976 ͑13͒ and 0.011 889 ͑12͒ MHz for the two species,
respectively. The constants calculated for the ground state
differed from the observed values by 0.000 007 6 MHz,
which was about seven times larger than the standard devia-
tion of the ground-state centrifugal distortion constant, as
ϭ373.444 98 ͑62͒ cmϪ1 with ␻eϭ373.444 86 ͑59͒ cmϪ1
.
B. Lowest excited electronic state
shown in Table II. The harmonic frequency ␻ is given by
e
(1/2␲)(k/␮)1/2 with k denoting the force constant and the
equilibrium centrifugal distortion constant De by
h3/ 32␲4k␮2r6 , and these two formulas, when combined
The observed spin–rotation interaction constant ␥ may
be used to estimate the excitation energy of the lowest ⌸
state. The ground-state ␥ value is Ϫ1072.598 MHz, which,
when inserted in the formula ␥ϭϪ4AB/⌬E, led to the ex-
citation energy Ϫ⌬E of 2771 cmϪ1, where the effective
͓
͔
e
with the expression for Be given in Eq. ͑5͒, lead to the fol-
lowing well-known relation:
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2856
J. Chem. Phys., Vol. 110, No. 6, 8 February 1999
C. Yamada and E. Hirota
the excited vibrational state at 387 cmϪ1 above the ground
state is 0.499 at the temperature of 527 °C. On the other
hand, the abundance of 87RbO relative to that of 85RbO is
0.386. The observed intensities are consistent with these
relative populations, confirming that the distribution of RbO
radicals in the absorption cell was close to the thermal one at
the cell temperature of 527 °C. Because we could not ob-
serve any spectral lines in the excited ⌸ state, its excitation
energy must be larger than 529 cmϪ1 ͑the relative population
of 87RbO corresponds to the Boltzmann factor of an excited
vibrational state at 529 cmϪ1 above the ground state͒. But, it
may not be as large as 2771 cmϪ1. If the large increase of ␥
with vibrational excitation is entirely ascribed to the reduc-
tion in energy separation, Ϫ⌬E is calculated to be 811.36
cmϪ1. This assumption requires, at the same time, the reduc-
tion in Franck–Condon factor, or in A constant, by a factor
of 0.293. It is also possible that higher excited electronic
states make positive contributions to the spin–rotation inter-
action constant, making its magnitude smaller and thus, the
energy separation apparently larger.
It has been demonstrated14 that the formula,
␥
ϭϪ4AB/⌬E, employed above to estimate the energy sepa-
ration ⌬E between the ⌺ and ⌸ states, holds only when an
identical potential applies to the both states, each described
by a single electron configuration. When the potential func-
tion is quite different for the two states, we must take into
account the Franck–Condon factor to calculate properly the
contribution of each vibrational state in the upper electronic
state. We have made such a calculation by using ab initio
values9 for the vibrational frequencies and the equilibrium
internuclear distances of the two states, which were fitted to
Morse potentials for the sake of simplicity. We have also
included the vibrational energy in the denominator, because
the energy separation between the two states is not much
larger than the vibrational energy.
The upper part of Fig. 4 shows the ␥ constants for the
␯Љϭ0 and 1 states thus calculated as functions of the excita-
tion energy Ϫ⌬E. As is usually done in most other cases,
we also assumed the spin-orbit coupling constant and the
rotational constant to be taken out as constants from the vi-
brational integrals. We have found that the effective spin-
orbit coupling constant of Ϫ50 cmϪ1, rather than Ϫ101 cmϪ1
as first assumed, gave a good fit to the observed data. The
FIG. 3. The Nϭ16←15 transitions of 85RbO in the ␯ϭ0 and 1 states and of
87RbO in the ␯ϭ0 state. The left and right insets show the F1 and F2 fine
structure spectra, respectively.
spin-orbit coupling constant A was assumed to be Ϫ101
cmϪ1 by referring to the results on LiO1, and the ground-
state rotational constant was used for B.
As listed in Table II, the spin–rotation interaction con-
stant increases in magnitude to Ϫ2051.828 MHz in the first
excited vibrational state. When a simple expression ␥ ϭ␥e
␯
Ϫ␣␥(␯ϩ 12) is used with ␯ denoting the vibrational quantum
number, the ‘‘equilibrium’’ spin–rotation interaction con-
stant ␥e is Ϫ582.983 MHz, which leads to the excitation
energy of 5098 cmϪ1
.
These two estimated values are much larger than the ab
initio results of 114 to 606 cmϪ1 ͑Refs. 7–10͒. The smallest
value, 114 cmϪ1, can be ruled out because spectral lines in
the excited vibrational state were clearly observed, whereas
those in the ⌸ state were not. The Boltzmann population in
TABLE II. Molecular constants of the rubidium monoxide radical ͑in MHz͒.a
85RbO, ␯ϭ0
85RbO, ␯ϭ1
7291.536 28 ͑86͒
87RbO, ␯ϭ0
Constant
B
7356.726 17 ͑42͒
7329.9967 ͑14͒
0.012 554 4 ͑38͒
0.0052 ͑31͒
Ϫ1068.40 ͑11͒
0.045 17 ͑18͒
Ϫ0.176 ͑14͒
610.7 ͑34͒
D
0.012 632 4 ͑11͒
Ϫ0.004 12 ͑84͒
Ϫ1072.598 ͑30͒
0.045 837 ͑50͒
Ϫ0.1512 ͑37͒
180.88 ͑38͒
0.013 967 6 ͑22͒
Ϫ0.1912 ͑17͒
Ϫ2051.828 ͑32͒
0.149 921 ͑75͒
Ϫ0.9651 ͑61͒
͓180.88͔
H/10Ϫ6
␥
␯
␥
D
␥H/10Ϫ5
b
c
42.4 ͑13͒
͓42.4͔
150.3 ͑96͒
eQq
T00
Ϫ28.0 ͑22͒
͓Ϫ28.0͔
Ϫ17.0 ͑12͒
0.102 ͑23͒
0.0326 ͑56͒
͓0.0326͔
␴
0.026
0.052
0.071
fit
aValues in parentheses denote standard deviations and apply to the last digits of the constants; those in square
brackets are fixed.
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J. Chem. Phys., Vol. 110, No. 6, 8 February 1999
C. Yamada and E. Hirota
2857
ϭ34 G, which are converted to the Fermi term bFϭbϩc/3
ϭ465 MHz, and a dipolar interaction constant cϭ143 MHz
in order to directly compare with the present results: 660.8
and 150.3 MHz, respectively.
When the Fermi term is compared with the 85Rb atomic
value 1037 MHz, as compiled by Morton and Preston15 for a
5s electron, the s character becomes quite large, 18.8%.
However, this is probably not the case; according to Lindsay
et al.,6 we should consider a 4s electron, rather than 5s elec-
tron, and then the s character would be close to 1% or so. It
is difficult to estimate the spin density from the observed c
constant, but the contribution of a 4p orbital would be of the
order of several thousand MHz and thus the observed c con-
stant would correspond to a spin density of a few percent, at
most.
The nuclear quadrupole coupling constant Ϫ28.0 MHz
determined for 85Rb may be compared with Ϫ70.3415 MHz
of 85RbF ͑Ref. 16͒, which is well known as an ionic mol-
ecule.
All of the observed hyperfine parameters are consistent
with the ionic configuration RbϩOϪ, with the unpaired elec-
tron predominantly occupying a p orbital mainly localized
␴
at the oxygen ion.
1 C. Yamada, M. Fujitake, and E. Hirota, J. Chem. Phys. 91, 137 ͑1989͒.
2 C. Yamada and E. Hirota, J. Chem. Phys. 99, 8489 ͑1993͒.
3 C. Yamada, M. Fujitake, and E. Hirota, J. Chem. Phys. 90, 3033 ͑1989͒.
4 E. Hirota, Bull. Chem. Soc. Jpn. 68, 1 ͑1995͒.
FIG. 4. The upper part shows the spin–rotation coupling constants for the
␯ ϭ0 and 1 states calculated as functions of the excitation energy Ϫ⌬E.
Љ
The effective spin-orbit coupling constant A was assumed to be Ϫ50 cmϪ1
The lower part displays ␥1 /␥0 , which indicates that Ϫ⌬E lies between 650
.
5 R. C. Spiker, Jr. and L. Andrews, J. Chem. Phys. 58, 713 ͑1973͒.
6 D. M. Lindsay, D. R. Herschbach, and A. L. Kwiram, J. Chem. Phys. 60,
315 ͑1974͒.
and 700 cmϪ1
.
7 J. N. Allison and W. A. Goddard III, J. Chem. Phys. 77, 4259 ͑1982͒.
8 J. N. Allison, R. J. Cave, and W. A. Goddard III, J. Phys. Chem. 88, 1262
͑1984͒.
lower part of Fig. 4 plots the ratio of the ␥ constants for
␯Љϭ1 and 0, ␥1 /␥0 , which may be regarded to be exempt
from the ambiguity of the spin-orbit coupling constant. We
have finally concluded from this calculation that the energy
9 S. R. Langhoff, C. W. Bauschlicher, Jr., and H. Partridge, J. Chem. Phys.
84, 4474 ͑1986͒.
10 S. P. So and W. G. Richards, Chem. Phys. Lett. 32, 227 ͑1975͒.
11 Y. Endo and E. Hirota, J. Chem. Phys. 86, 4319 ͑1987͒.
12 E. Hirota, High Resolution Spectroscopy of Transient Molecules
͑Springer, Heidelberg, 1985͒.
difference Ϫ⌬E lies between 650 and 700 cmϪ1
.
13 A. G. Maki and W. B. Olson, J. Mol. Spectrosc. 140, 185 ͑1990͒.
14 H. Lefebvre-Brion and R. W. Field, Perturbations in the Spectra of Di-
atomic Molecules ͑Academic, Orlando, 1986͒.
C. Electronic structure
Lindsay et al.6 reported hyperfine constants, isotropic as
well as anisotropic, of 87RbO in a matrix, aϭ166 G and Tʈ
15 J. R. Morton and K. F. Preston, J. Magn. Reson. 30, 577 ͑1978͒.
16 C. D. Hollowell and F. Lange, Z. Naturforsch. A 29, 1548 ͑1974͒.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP:
202.28.191.34 On: Sat, 20 Dec 2014 15:13:40