Rotational spectroscopy of ethylamine into the THz

Zbigniew Kisiel, Adam Kraśnicki

Institute of Physics, Polish Academy of Sciences

Ivan R. Medvedev, Christopher Neese, Sarah Fortman, Manfred Winnewisser, Frank C. De Lucia

Department of Physics, The Ohio State University

Holger S. P. Müller

I. Physikalisches Institute, Universitat zu Köln

64th OSU International Symposium on Molecular Spectroscopy TC0964th OSU International Symposium on Molecular Spectroscopy TC09

Ethylamine:

a = 1.057(6) Db = 0.764(9) Dc = 0 D

a = 0.11(1) Db = 0.65(1) Dc = 1.014(15) D

Anti Gauche

DE (Gauche-Anti) = 50 – 100

cm-1

anti, cmw: Fischer + Botskor, J.Mol. Spectrosc. 91, 116 (1982)gauche, cmw: Fischer + Botskor, J.Mol. Struct. 97, 93 (1983)

Fischer + Botskor, J.Mol. Spectrosc. 104, 226 (1984)

anti, 10-270 GHz: Apponi et al., Astrophys. J. 673, 1240 (2008)

gauche-Ethylamine:

Fischer and Botskor, J.Mol.Struct. 97, 93 (1983) Fischer and Botskor, J.Mol.Spectrosc. 104, 226 (1984)

+ torsion

o = antisymm.e = symm.

Etors 1170.6(2) MHz

Einv 1391.4(2) MHz

rotation

+ inversion

a = antisymm.s = symm.

(+ CH3 torsion ? )

Rotational transitions in gauche-Ethylamine:

Fischer and Botskor, J.Mol.Struct. 97, 93 (1983) Fischer and Botskor, J.Mol.Spectrosc. 104, 226 (1984)

Ea 220.8(2) MHz

Es 2562.0(2) MHz

b within each of the four substates

c between substates with different torsional parity but in the same inversion state

1

1

3

3

FASSST = FAst Scanning Submillimeter Spectroscopic Technique

Tripled:780 - 1125 GHz one source, two

triplers

3x

Standard:110 - 370 GHz three sources

260 GHz 375GHz

Coverage of the ethylamine spectrum:

FASST: 115 - 376 48 x 12 GHz synthesizer:

552 – 658 GHz

3 x FASST: 868 - 1081

Comparison with predictions:

a-type: mainly anti b- and c-type: mainly gauche

298 K

Intensity correction at 1 THz using SO2 lines:

900 1000 GHz

Derived signal level

Noise patch

Raw

Corrected

Intensity correction at 560 GHz using power signal:

Apparent line intensity is divided by the power signal and the result is compared with CDMS and JPL database linelists.

Intensity correction at 560 GHz using power signal:

A

A – line in main Q-type sequence that becomes too attenuated by correction (kink in power)

B

B – R-type interloper that seems poorly predicted (but the one to high frequency from it is fine)

AABS has been applied to many different types of broadband spectra: FASSST, cascaded multiplication THz, chirped pulse FTMW, Bruker FTIR..

Understanding of the spectrum (600 GHz):

Anti, bRGauche, cR, ae ao

Gauche: Ka=1312 cQ-branch,ao ae transitions

Understanding of the spectrum (1 THz):

Gauche, cR, ao ae

Gauche, cR, ae ao

SO2

Anti, bR

The major spectroscopic constants for ethylamine:

_____________________________________________________________________________________________

ANTI GAUCHE GAUCHE AE AO SE SO_____________________________________________________________________________________________

A /MHz 31758.1834(98) 32398.43(41) 32404.03(40) 32416.13(10) 32386.49(10) B /MHz 8749.2537(20) 8937.43(14) 8938.51(14) 8934.34(18) 8933.15(18) C /MHz 7798.9522(22) 7829.30(14) 7829.24(14) 7833.47(18) 7833.49(18) DJ /kHz 7.6378(10) 7.9369(21) 7.9988(22) 7.9888(45) 7.9819(50) DJK /kHz -27.088(23) -33.05(18) -27.69(15) -26.77(23) -32.86(24) DK /kHz 191.158(56) 219.5(29) 186.5(29) 198.4(40) 200.1(43) delJ /kHz 1.4156(12) 1.6575(60) 1.6804(58) 1.7088(19) 1.7137(21) delK /kHz -1.761(55) -44.2(16) -32.5(17) 14.82(35) 11.84(38) DE /MHz 220.67(22) 2561.67(17) Ga /MHz 181.66(25) 62.0(22) Fbc /MHz 64.4(12) 93.9(11) Gb /MHz 15.6(43) 25.3(31) Nlines 866 1586 366 sigma /MHz 1.5 1.8 0.8 max K_a 16 14 4 max f /GHz 1059 1057 651_____________________________________________________________________________________________

unscaled B3LYP/6-31G(d,p) 7.568 7.756 -29.79 -31.28 196.1 205.3 1.382 1.592 2.686 10.92

Anti-ethylamine: problems with higher-J transitionsJ = 37 36, aR

Ka = 3

12

14

16

18

22

Anti-ethylamine: unresolved problems even at low-J and Ka:

Apponi et al., Astrophys. J. 673, 1240 (2008)

Room temperature rotational spectrum of ethylamine was recorded up to 1081 GHz in three broadband segments.

Rotational transitions in the anti conformer and in the gauche ae and ao substates have been assigned and fitted for frequencies of well over 1 THz. For the gauche se and so substates the assignment reached 650 GHz.

The strongest features in the 600GHz and 1 THz regions are accounted for.

This is very much a work in progress:

gauche: many transitions have been confidently assigned by using the Fischer+Botskor model of two coupled pairs of states but not yet well fitted

anti: many unresolved problems at high Ka and even low-J, low-Ka

The next step will be to set up the full quartet of interacting inversion+torsion substates for the gauche rotamer.

SUMMARY: