1. 1Kanagawa Institute of Technology 3Georgia Southern University
The differences in the role of O and S atoms in the molecular structure and dynamics of some complexes
Yoshiyuki Kawashima,1 Akinori Sato,1 Yoshio Tatamitani,1 Nobuyuki Ohashi,2 James M. Lobue,3 and Eizi Hirota4
1Kanagawa Institute of Technology
2Kanazawa University
3Georgia Southern University
4The Graduate University for Advanced Studies

2. Ar–dimethyl sulfide (DMS) CO–ethylene oxide (EO)
Purpose
We have investigated van der Waals complexes containing of either one of a rare gas atom, CO, N2, or CO2 combined with one of the two pair molecules: DME/DMS and EO/ES by using a FTMW spectrometer,
　　in order to examine how different the role of the O and S atoms is in molecular properties of the complex.
The present talk reports the results on Ar-DMS and CO-EO, in comparison with those on Ar-DME and CO-ES, respectively.
Ar–dimethyl sulfide (DMS)
CO–ethylene oxide (EO)

3. Potential of the tunneling motion for Rg-DME complexes；Rg = Ne, Ar and Kr
The large amplitude motion is expected in the weak van der Waals complex. Rg
C2v a
Rc.m.
E / cm–1
Ne–DME: 16 cm–1
Ar–DME: 58 cm–1
Kr–DME: 112 cm–1
Binv 1–
v = 1+
Binv:
Barrier to inversion
807.2(9) MHz
0.9980(6) MHz
0.26 (5) MHz 0–
v = DE 0+
a / deg

4. CO-dimethyl ether (DME) complex1)
Heavy-atom skeleton of CO-DME was essentially planar. The carbon atom of CO is closer to DME than the O atom.
The splitting between the two sets of the same transition varied from 2 to 15 MHz, and the two components were assigned to the two lowest states of the internal rotation of CO with respect to DME governed by a twofold potential.
The bond distance between the center of mass is 3.68 Å. The van der Waals bonding of CO- DME is weak and is between those of Ne- DME and Ar-DME.
75.7°
Rc.m. = 3.68 Å
1) Y. Kawashima et al, J. Chem. Phys. 127, (2007)

5. Instrument: Fourier transform microwave spectrometer
Experimental
Instrument: Fourier transform microwave spectrometer
Sample : 1% DMS diluted with Ar
or 0.5% EO and 1.5% CO diluted with Ar
Backing pressure : 1.0 atm Shots : 20
Frequency region : 3.7~25 GHz Step : 0.25 MHz
Vacuum chamber
Mirror (fixed)
Supersonic molecular
beam injection
Molecular beam injection nozzle MW
Mirror (mobile)
sample
Diffusion pump
Rotary pump

6. Observed spectra of Ar-DMS
Ar–DMS (normal)
221 – 111
a(vdW)
c(vdW)
b(DMS)
7050
7100
7150
7200
7250
7300
7350
Spectrum of Ar–DME
212(+) – 202(–)
212(–) – 202(+)
111(+) – 101(–)
111(–) – 101(+)
DE ≈ 1 MHz
18000
18200
18400
18600
18800
19000
220 – 110
No splitting due to the large amplitude motion is found!
Ar–DMS (34S)
Ar–DMS (13C)
220 – 110
221 – 111
220 – 110
221 – 111
Frequency / MHz

7. Observed spectra of the a-type and c-type transitions of Ar-DMS
a-type transition
505–404 EE
c-type transition
211–101
AA EE
AE EA AE EA
9823.9
9824.4 AA
Frequency / MHz
Frequency / MHz
V3 = (32) cm-1
(V3 = cm-1 for DMS monomer)

8. Observed spectra of the forbidden transitions of Ar-DMS

9. Phenomenological Hamiltonian
The first-order Coriolis term
where

10. Molecular constants and the substituted coordinates of the S and C atoms in Ar-DMS
Ar–DMS (normal)
Ar–(CH3)234S
Ar–13CH3SCH3
A / MHz
(22)
(20)
(42)
B / MHz
(71)
(11)
(24)
C / MHz
(10)
(12)
(27)
DJ / kHz
(46)
(48)
5.6862(11)
DJK / kHz
(45)
39.210(7)
40.275(15)
DK / kHz
–39.911(19)
–38.075(24)
–39.77(8)
dJ / kHz
(16)
(17)
(32)
dK / kHz
25.669(24)
24.52(5)
25.15(12)
FK / kHz
0.0962(24) –
<1|q|2> / MHz
(11)
Na-type / - 43 16
Nc-type / - 79 39 25
s / kHz
3.8
0.6
rs coordinates
as (S or C) / Å
1.5713
1.3420
bs (S or C) / Å i
±1.3707
cs (S or C) / Å
0.5684
0.5713

11. Observed rotational spectra of CO-EO in Ar
J = 5←4
CO-EO complex
a-type R-branch transitons
J = 1←0
c-type R-branch transitions
EO monomer
c-type Q-branch transitions
Ar-EO complex
J = 4←3
J = 2←1
J = 3←2
8000
20000
10000
12000
14000
16000
18000
11200
11300
11400
11500
11600
J = 1 5
CO-EO complex
C-type Q-branch transitions(Ka=1←0)
8000
20000
10000
12000
14000
16000
18000
Frequency / MHz

12. Observed rotational spectra and obtained molecular constants of CO-EO complex
The a-type and strong c-type transitions of CO-EO complex were observed, however, no b-type transition was found.
The rotational and centrifugal distortion constants of CO-EO were determined using an asymmetric top Hamiltonian.
　404–303
(a-type transition)
MHz
normal
A /MHz
(7)
B /MHz
(8)
C /MHz
(9)
DJ /kHz
9.7986(10)
DJK /kHz
44.185(5)
DK /kHz
83.41(13)
d1 /Hz
–3.04(7)
d2 /Hz
46.2(7)
N (a-type) 33
N (c-type) 34
s /kHz
1.98
Frequency / MHz
110–000
(c-type transition)
MHz
Frequency / MHz

13. Molecular constants and the substituted coordinates of the O and C atoms of five isotopomers of CO–EO complex
normal
CO–EO(13C)
CO–EO(18O)
13CO–EO
C18O–EO
A /MHz
(7)
(4)
(26)
(11)
(4)
B /MHz
(8)
(9)
(4)
(31)
(6)
C /MHz
(9)
(11)
(7)
(18)
(6)
DJ /kHz
9.7986(10)
9.5212(16)
9.686(11)
9.4950(24)
9.0345(9)
DJK /kHz
44.185(5)
44.183(13)
43.96(14)
40.326(11)
(33)
DK /kHz
83.41(13)
[83.41] a
86.76(23)
90.96(9)
d1 /Hz
–3.04(7)
15.2(5)
20.95(20)
10.01(5)
d2 /Hz
46.2(7)
38.8(13)
48.9(12)
40.2(4)
Pbb /uÅ2
N (a-type) 33 16 11 31
N (c-type) 34 14 12 19 21
s /kHz
1.98
1.03
5.59
3.12
1.20
0.057
0.030
rS coordinates
|C(a)| or |O(a)/Å
1.613
1.613
1.771
2.498
0.054 i
|C(b)| or |O(b)/Å
0.739
0.739
0.584
0.270
|C(c)| or |O(c)/Å
0.280

14. Observed and ab initio calculated two structural parameters, stretching force constants, and binding energy or Ar-DMS and related molecules
[I aa(vdW) and Ibb(vdW)]
[Ibb(vdW) and Icc (vdW)]
[Iaa(vdW) and Icc(vdW)] Ne a a Ar a
Rcm
Rcm a
Rcm Ar
Rcm Ne
Ne–DME
Ar–DME
Ne–DMS
Ar–DMS

15. cm–1
t / degrees
Rc.m. a t
a / degrees

16. Summary Ar CO DME DMS EO ES R(O-Ar)=3.382Å R(O-C)=3.047Å 106.8 °
ks=2.30 Nm-1
ks=1.40 Nm-1
R(S-C)=3.49Å
R(S-Ar)=3.989Å
DMS
66.9 °
75.7 °
ks=2.00 Nm-1
ks=2.70 Nm-1
R(O-Ar)=3.476Å
R(O-C)=3.00Å EO
93.0 °
97.7 °
ks=2.20 Nm-1
ks=3.30 Nm-1
R(O-Ar)=3.974Å
R(S-C)=3.47Å ES
70.7 °
74.6 °
ks=2.10 Nm-1
ks=3.20 Nm-1

17. Summary CO HF DME DMS EO ES 7.2 º R(O-C)=3.047Å 137.1 ° ks=1.40 Nm-1
R(S-C)=3.49Å
DMS
75.7 °
ks=2.70 Nm-1
16.5 °
R(O-C)=3.00Å EO
108.0 °
97.7 °
ks=3.30 Nm-1
R(S-C)=3.47Å ES
16.8 °
86.5 °
74.6 °
ks=3.20 Nm-1

18. Conclusion
1) In the case of the CO-DMS and CO-ES, the CO moiety is located closer to the CH3 and CH2 end of DMS and ES, respectively, whereas to the O end in the cases of CO-DME and CO-EO.
2) Similar differences were found for Rg complexes. Because of the larger atomic radius and lower electronegativity of S than those of O, S behaves as a much weaker nucleophile than O.
3) The structures of Rg-DMS and Rg-ES thus considerably deviate from that of the n-type complex proposed by Legon.
A.C. Legon, Angew. Chem. Int. Ed. 38 (1999) 2686.