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 CO 2 –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 CS 2 –DME 3) 1) P. Ottaviani et al, ChemPhysChem. 5, (2004) 2) P. Ottaviani et al, Chem. Phys. Lett. 394, (2004) 3) S. A. Peebles et al, Chem. Phys. Lett. 410, (2005) 4) J. J. Newby et al, J. Phys. Chem. A. 108, (2004) 5) J. J. Newby et al, J. Phys. Chem. A. 108, (2004) However, CO-DME has a different structure with single vdw bondings.

CO–dimethyl ether (DME) complex 1) 75.7 ° R c.m. = 3.68 Å 1) Y. Kawashima et al, J. Chem. Phys. 127, (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 spectrometer Sample : 0.5% DMS or ES + 1.5% CO diluted with Ar Backing pressure : 3 atm Frequency region : 6 ~ 30 GHz

Observed rotational spectra in CO / DMS /Ar system ・ DMS ・ Ar–DMS ・ CO–DMS Frequency /GHz c-type Q-branch K a = 3 ←

Frequency /MHz c-type Q-branch transition 3 30 – – – – – – – – – – – 5 23

Observed rotational spectra in CO / ES /Ar system b-type Q-branch K a = 2 ← 1 K a = 3 ← 2 Frequency /GHz ・ ES ・ Ar–ES ・ CO–ES

/ MHz / MHz / MHz / MHz CO–DMSCO–ES 50 shots MHz 50 shots MHz 5 05 –4 04 (a-type transition) 6 06 –5 15 (b-type transition) MHz 6 06 –5 05 (a-type transition) MHz 2 21 –1 11 (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–DMSCO–ES A /MHz (4) (18) B /MHz (15) (8) C /MHz (13) (8)  J /kHz (10) (3)  JK /kHz (6) (24)  K /kHz –51.88(4) –9.352(17)  J /kHz (4) (13)  K /kHz 25.54(3) 9.26 (3) N (a-type) N (b-type) － 67 N (c-type) 55 －  rms /kHz 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 MHz a–type transition (6 06 –5 05 ) AE+EA AA EE V 3 /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.

Forbidden transition of CO–DMS – – – –3 22 / MHz Allowed transitions (c–type transitions) Forbidden transitions (b–type transitions)

b a Planar moment of inertia DMS (monomer)CO–DMS ES (monomer)CO–ES P aa /uÅ P bb /uÅ P cc /uÅ a c a 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) (4) (6) (10) 25.54(3) (4) (5) 50.99(2) [-51.89] [0.5531] [25.52] [5.6653] [52.592] [-51.89] [0.5531] [25.52] (14) (10) (5) (6) 22.57(4) (8) (6) (2) (4) 24.14(3) a (4) (15) (13) a)The number in parentheses denotes 3 . b)Fixed at the values for the normal species. /MHz /kHz

normal CO–(CH 2 ) 2 34 SCO–CH 2 S 13 CH 2 CO–ESC 18 O–ES A / MHz (18) (19) (17) (20) (22) B (8) (9) (4) (14) (7) C (7) (10) (4) (14) (8)  J / kHz5.6088(3)5.5606(4) (4) (6)5.1310(4) JK (24)16.430(3) (27) (4) (27) K –9.352(17) –9.58(4)–10.01(3) –7.502(27)–6.56(5) J (13) (3)0.4745(4) (3) (19) K 9.26(3) 9.80(4)[9.26] 8.80(6)8.782(28) P cc / uÅ N a-a- type / - N b-b- type     b / MHz / 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–DMSCO–ES C (CO) OSC (DMS) C (CO) OSC (ES) |a| /Å |b| /Å i |c| /Å i0.740 r s coordinates of CO–DMS and CO–ES b a R c.m. =3.80 Å c R c.m. = 3.79 Å a CO–DMS complexCO–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–DMSCO–ES experimental ab initio a) experimental ab initio a) A /MHz (4) (18) B /MHz (15) (8) C /MHz (13) (8)  /deg  /deg r (S–C) /Å CO–DMS CO–ES a  Calculated by ab initio MO calculation at the MP2/6−311++G(d,p) level.

Comparison of force constants and binding energies for several complexes complexes k s / Nm –1 E B / kJ mol –1 R c.m. / Å CO–DME Ar–EO Ar–DMS Ar–ES Ar–DME CO–DMS CO–ES CO 2 –DME Force constantBinding 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.

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