Fourier transform microwave spectra of

CO–dimethyl sulfide and CO–ethylene sulfide

Akinori Sato, Yoshiyuki Kawashima and Eizi Hirota*

The Graduate University for Advanced Studies*

Kanagawa Institute of Technology

Introduction

CO2–DME 4) OCS–DME 5)

Several complexes containing dimethyl ether (DME) have been investigated.

singly vdW bonding triply vdW bonding

HX–DME 1,2)

X = F, Cl

X

CS2–DME 3)1) P. Ottaviani et al, ChemPhysChem. 5, 336-341 (2004)2) P. Ottaviani et al, Chem. Phys. Lett. 394, 262-265 (2004)3) S. A. Peebles et al, Chem. Phys. Lett. 410, 77-81 (2005)4) J. J. Newby et al, J. Phys. Chem. A. 108, 11234-11240 (2004)5) J. J. Newby et al, J. Phys. Chem. A. 108, 7372-7378 (2004)

However, CO-DME has a different structure with single vdw bondings.

CO–dimethyl ether (DME) complex1)

75.7°

Rc.m. = 3.68 Å

1) Y. Kawashima et al, J. Chem. Phys. 127, 194302 (2007)

Heavy-atom skeleton of CO-DME was

essentially planar. The carbon atom of CO is

closed to DME.

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 between those of Ne-DME and

Ar-DME.

Molecular conformations of DMS and ES complexes containing CO and to study the stability of conformer ? How strong is van der Waals bonding? To study the difference between oxygen and sulfur atoms.

Aim of the present investigation

Introduction

ethylene oxide (EO) ; oxirane

ethylene sulfide (ES) ; thiirane

dimethyl sulfide (DMS)

Experimental

Instrument : Fourier transform microwave spectrometerSample : 0.5% DMS or ES + 1.5% CO diluted with ArBacking pressure : 3 atmFrequency region : 6 ~ 30 GHz

Observed rotational spectra in CO / DMS /Ar system

・ DMS

・ Ar–DMS・ CO–DMS

Frequency /GHz

c-type Q-branch Ka = 3 ← 2

14 20

19200 20000Frequency /MHz

c-type Q-branch transition

3 30 –

322

4 31 –

423

5 32 –

524

7 35 –

725

6 34 –

624

4 32 –

422

3 31 –

321

6 33 –

625

7 34 –

726

8 35 –

827

5 33 –

523

　 15 20 25 30

Observed rotational spectra in CO / ES /Ar system

b-type Q-branch

Ka = 2 ← 1

Ka = 3 ← 2

Frequency /GHz

・ ES

・ Ar–ES

・ CO–ES

17990.0 17990.6 / MHz

14048.4 14049.4 / MHz

18203.8 18204.6 / MHz

15935.6 15936.4 / MHz

CO–DMS CO–ES

50 shots14048.8650 MHz

50 shots

15935.9888 MHz

505–404 (a-type transition)

606–515 (b-type transition)

18204.1904 MHz

606–505 (a-type transition)

17990.3102 MHz

221–111 (c-type transition)

1000 shots

50 shots

a-type transitions were split into a triplet

No b-type transitions were observed.

→ Dipole moment b ≈ 0

No c-type transitions were observed.

→ Dipole moment c ≈ 0

Rotational spectra of CO–DMS and CO–ES

CO–DMS CO–ES

A /MHz 5460.4722(4) 7623.22255(18)

B /MHz 1609.50223(15) 1668.39787(8)

C /MHz 1452.08187(13) 1528.97614(8)

J /kHz 5.6660(10) 5.6088(3)

JK /kHz 52.590(6) 16.8610(24)

K /kHz –51.88(4) –9.352(17)

J /kHz 0.5526(4) 0.49065(13)

K /kHz 25.54(3) 9.26 (3)

N (a-type) 19 42

N (b-type) － 67

N (c-type) 55 　　　 －

rms/kHz 5.4 2.7

Molecular constants of CO–DMS and CO–ES a)

a) The number in parentheses denotes 3.

Transition frequencies were fitted to the “asymmetric top Hamiltonian”.

Internal rotation of methyl group of CO–DMS

18204.0 18204.4 MHz

a–type transition (606–505)

AE+EA AA

EE

V3 /cm–1 Ref.

DMS (monomer) 752.6(8) Y. Niide et al, Mol.Spectrosc.,220(2003)65-79

CO–DMS 720 (30) This work

DME (monomer) 956.5(29) Y. Niide et al, Mol.Spectrosc.,220(2003)65-79

CO–DME 722(2) Y. Kawashima et al, J. Chem. Phys. 127(2007)

• The three components of the inertial rotation of the two methyl groups were observed.

• Using the Hamiltonian of the equivalent two tops of the methyl groups, written by late Hayashi, the observed splittings were analyzed.

19627.8 19628 19628.2

Forbidden transition of CO–DMS

330

331

321

322

330

331

321

322

19651.4 19651.6 19651.8

331–321 330–321 330–322

331–322

/ MHz/ MHz

Allowed transitions (c–type transitions)

Forbidden transitions (b–type transitions)

b

a

Planar moment of inertia

i

iicci

iibbi

iiaa cmPbmPamP 222 ,,

DMS (monomer) CO–DMS ES (monomer) CO–ES

Paa /uÅ2 63.162 284.7413 43.3266 278.7751

Pbb /uÅ2 25.225 63.2964 19.6394 47.4538

Pcc /uÅ2 3.151 29.2558 3.3600 19.4939

a

ca

b

CO–ES CO–DMS

a

b

→ CO moiety in CO-DMS or CO-ES located bisecting the CSC angle of DMS or ES.

Molecular constants for five isotopomers of CO–DMS a, b)

normal CO – (CH3)234S CO – CH3S

13CH313CO – DMS C18O – DMS

A /MHz 5460.4722(4) 5418.1037(3) 5337.3383(1) 5443.2763(5) 5418.0018(2)B 1609.5023(1) 1593.5151(2) 1600.5945(1) 1584.1605(2) 1528.1378(1)C 1452.0812(2) 1442.0904(2) 1438.2738(1) 1432.5943(2) 1386.1367(1)Δ J /kHzΔ JK

Δ K

δ J

δ K

P bb /uÅ2

N a- type /-

N c- type

-51.88(4)52.590(6)5.6660(10)

25.54(3)63.30

0.5526(4)

1955

5.575(5)50.99(2)

[-51.89][0.5531]

[25.52]

63.290

16

[5.6653][52.592]

65.16

[-51.89][0.5531]

[25.52]

08

5.4573(14)49.4710(10)

-48.42(5)0.5244(6)

22.57(4)63.23

747

5.2328(8)49.920(6)

-48.60(2)0.4843(4)

24.14(3)63.58

942

a

5460.4722(4)1609.50233(15)1452.08187(13)

a) The number in parentheses denotes 3.b) Fixed at the values for the normal species.

/MHz/MHz

/kHz/kHz/kHz/kHz

normal CO–(CH2)234

S CO–CH2S13

CH213

CO–ES C18

O –ES

A / MHz 7623.22255(18) 7474.86931(19) 7488.84943(17) 7591.73545(20) 7610.18115(22)B 1668.39787(8) 1655.85682(9) 1656.25673(4) 1644.36900(14) 1581.49720(7)C 1528.97614(7) 1512.37126(10) 1518.15570(4) 1507.56272(14) 1455.20392(8) J / kHz 5.6088(3) 5.5606(4) 5.4666(4) 5.4275(6) 5.1310(4)

JK 16.8610(24) 16.430(3) 16.9620(27) 15.504(4) 15.2165(27)K –9.352(17) –9.58(4) –10.01(3) –7.502(27) –6.56(5)

J 0.49065(13) 0.5059(3) 0.4745(4) 0.4755(3) 0.43092(19)K 9.26(3) 9.80(4) [9.26] 8.80(6) 8.782(28)

P cc / uÅ2 19.3366 19.3270 19.8637 19.3398 19.337442 0 0 16 2267 38 29 35 42

N a- type / -Nb- type

b

/ MHz/ MHz

/ kHz/ kHz/ kHz/ kHz

/ -

Molecular constants of five isotopomers of CO–ES a, b)

a) The number in parentheses denotes 3.b) Fixed at the values for the normal species.

CO–DMS CO–ES

C(CO) O S C(DMS) C(CO) O S C(ES)

|a| /Å 2.183 2.904 1.111 1.214 2.110 2.914 1.083 1.303

|b| /Å 0.044 0.068 0.063 i 1.370 0.528 0.248 0.828 0.812

|c| /Å 0.546 0.303 0.615 0.538 0.058 0.021 0.072 i 0.740

rs coordinates of CO–DMS and CO–ES

b

a

Rc.m.=3.80 Å

c

Rc.m. = 3.79 Å

a

CO–DMS complex CO–ES complex

Comparison of molecular constants with experimental and ab initio MO calculation

= 67.0°

r(S–C) = 3.47 Å

74.6°= 69.1°

r(S–C) = 3.49 Å

75.7°

CO–DMS CO–ESexperimental ab initio a) experimental ab initio a)

A /MHz 5460.4722 (4) 5438.4 7623.22255(18) 7548.9 B /MHz 1609.50233 (15) 1602.3 1668.39787(8) 1694.4 C /MHz 1452.08187 (13) 1457.4 1528.97614(8) 1549.2/deg 　　 75.7 77.7 74.6 72.9 /deg 　　 69.1 68.9 67.0 68.8 r(S–C) /Å 3.49 3.53 3.47 3.49

CO–DMS CO–ES

aCalculated by ab initio MO calculation at the MP2/6−311++G(d,p) level.

Comparison of force constants and binding energies for several complexes

JhD

CBCBCBRμπ ])()(44[)(16 224424 c.m.

sk

2c.m.72

1Rks

BE

　 complexes ks / Nm–1 EB / kJ mol–1 Rc.m. / Å

CO–DME 1.4 1.6 3.68Ar–EO 1.5 1.6 3.61

Ar–DMS 2.0 2.4 3.80Ar–ES 2.1 2.5 3.79

Ar–DME 2.3 2.5 3.53CO–DMS 2.7 3.3 3.79

CO–ES 3.2 3.9 3.80

CO2–DME 10.9 9.7 3.26

Force constant

Binding energy

　 Observation of the rotational spectrum of CO–EO complex.

Molecular constants of five isotopomers were determined.

CO moiety in CO–DMS is located in a plane perpendicular to the C-S-C plane and bisecting the CSC angle of DMS.

Force constant and binding energy of CO–DMS were estimated.

Summary

Future works

CO–ES

CO–DMS

Molecular constants of five isotopomers were determined.

CO–ES has a similar structure to CO–DMS.

Force constant and binding energy of CO–ES were estimated.

Thank you for your attention!Thank you for your attention!