+MILLIMETER-WAVE SPECTROSCOPY OF ETHYLMERCURY HYDRIDEManuel Goubet, Roman A. Motiyenko, Laurent MargulèsLaboratoire PhLAM, Université Lille 1Jean-Claude GuilleminsSciences Chimiques de Rennes - ENSCR

+Chemistry background

Synthesis of organomercury compounds: Guillemin, J.-C.; Bellec, N.; Kiz-Szetsi, S.; Nyulaszi, L.;

Veszpremi, T. Inorg. Chem. 1996, 35, 6586−6591. Craig, P. J.; Garraud, H.; Laurie, S. H.; Mennie, D.; Stojak, G.

H. J. Organomet. Chem. 1994, 468, 7−11.

Extensive spectroscopic and ab initio study of gaseous HgH2 and HgD2: Shayesteh, A.; Yu, S.; Bernath, P. F. J. Phys. Chem. A 2005,

109, 10280−10286.

+Ab initio structure of C2H5HgH

Method: MP2(full)

Basis sets: Hg - small core pseudo-

potential basis set: cc-pVTZ-PP, accounting for relativistic effects

C - cc-pCVTZ with extra core/valence functions

H - standard cc-pVTZ

Geometry optimization using « tight » convergence option

207.8 pm

161.5 pm

153.1 pm

113.5°

A = 29464.95 MHzB = 2817.15 MHzC = 2654.66 MHz

μa = 0.43 D; μb = 0.13 D

+The Lille fast scan spectrometer

BWOHV

PowerSupply

F/32+IF

Amplifier

Absorbing cell

DDS8.7 – 11.8

MHz

SR7270DSP Lock-

in amplifier

Bolometer

RS-232

SynthesizerAgilent E8257D

8 – 16.5 GHz

PLL,IF=8.7 –

11.8MHz

Amplifier

RS-2

32

Internal bus

Microcontroller ADuC 842

Ethernet

fast frequency switchingup to 20 μs/point

frequency range in this study: 120 – 180 GHz

Frequency synthesize

r Absorbing cell

Bolometer

to diffusion+

rotary pump

Sample at 250 K

At room temperature

+The spectrum

5.34 GHz ≈ B+C

f = (B+C)(J+1)

202Hg

201Hg

200Hg199Hg

198Hg204Hg

ν23 = 1 excited stateω= 199 cm-1

ab initio: B+C = 5.45 GHZ

201Hg I = 3/2

ν22 = 1 excited stateω= 233 cm-1

V3 = 1100 cm-1

CH3 top internal rotation ?

17 GHz spectrum recorded in ≈20 min (0.024 MHz frequency step)

+Calculation of nuclear quadrupole tensor

pseudo-potential should not be used

however high-level all electrons calculations of the electric field gradient for an atom like Hg might become unreasonably time consuming

the solution is to perform low level field gradient calculations (B1LYP/6-311G(df,p)) based on the geometry from high level calculations (see W.C. Bailey web-page at http://nqcc.wcbailey.net/)

F=? ??

?

+Calculation of nuclear quadrupole tensor Calculations have been made at the the HF, B1LYP and B3LYP levels

of theory

Basis sets: Hg - all electrons ANO-RCC C and H – cc-pVDZ, 6-311G(df,p), cc-pVTZ and ANO-RCC

For the consistency of the basis set over the molecule, the initial ANO basis was reduced to a double- or triple-zeta polarization according to the set used for H and C

The two-electrons integrals were calculated using the second order Douglas-Kroll-Hess (DKH) Hamiltonian to take into account the relativistic effect

The input geometry was the atomic Cartesian coordinates calculated at the MP2/cc-pVTZ-PP in the principal inertial axis orientation

+Calculation of nuclear quadrupole tensor: the results

The agreement is improving faster by increasing the level of the method than the quality of the basis set

If one has to compromise between accuracy and calculations time, the best choice would be a combination of a high level method and a small basis set

χaa

χbb

HF B1LYP B3LYPExperiment

cc-pVDZ

(126)

-1962

786

-1545

617

-1517

606

-1169.50(67

)

473.33(61)

6-311G(df,p)

(154)

-1956

784

-1532

612

-1503

600ANO-DZP

(180)

-1953

782

-1513

603

-1481

590cc-pVTZ

(237)

-1919

778

-1467

585

-1435

572ANO-TZP

(291)

-1942

778

-1415

562

-1376

546

63/2 – 61/257/2 – 55/2

61/2 – 59/259/2 – 57/2

+Calculation of nuclear quadrupole tensor: the results The angle between principal axis a and internuclear axis z

containing quadrupolar atom (Legon, A. C. Faraday Discuss. 1994, 97, 19):

χab can be estimated from the diagonal components in the assumption that the angular oscillation of the subunit containing the quadrupolar nucleus is two-dimensionally isotropic in the ab plane:

Estimation: χab = 644.78 MHz and αaz= 19.1°

From ab initio calculations: αaz = 19.6°

+Rotational spectroscopy: the results

202Hg 200Hg 199Hg 201Hg 198Hg 204Hg

A /MHz 29302.2001(35)

29464.946

29302.823(13) 29303.129(11) 29302.57(19) 29303.509(44) 29301.593(56)

B /MHz 2750.73634(10)

2817.149

2753.73409(19)

2755.25383(17)

2752.22888(73)

2756.79080(44)

2747.79563(50)

C /MHz 2593.295144(97)

2654.657

2595.96453(19)

2597.31756(17)

2594.62014(57)

2598.68407(43)

2590.67525(49)

ΔJ /kHz 1.349427(53)

1.372

1.352251(62) 1.353555(61) 1.35144(20) 1.355191(96) 1.34668(11)

ΔJK /kHz -28.73258(74)

-29.288

-28.76191(78) -28.77643(82) -28.7520(23) -28.7924(11) -28.7069(15)

ΔK /kHz 514.23(20)

496.021

513.07(94) 513.00(57) 514.23 516(16) 514.23

δJ /kHz 0.148784(10)

0.154

0.149193(44) 0.149477(45) 0.14952(16) 0.149911(88) 0.14848(12)

δK /kHz 6.1780(76)

6.127

6.241(28) 6.200(32) 6.64(10) 6.392(65) 6.270(62)

HKJ /Hz -2.0210(36) -2.0265(38) -2.0346(44) -1.996(11) -2.0342(56) -2.0291(99)

LKKJ /mHz 0.1296(43) 0.1334(48) 0.1467(60) - 0.1419(76) 0.143(16)

N lines 561 537 483 559 449 395

Jmax; Kmax 52; 26 51; 26 43; 24 34; 16 46; 25 34; 22

σ /MHz 0.024 0.023 0.019 0.041 0.027 0.026

+