ANALYSIS OF THE ROTATIONAL STRUCTURE IN THE HIGH-RESOLUTION INFRARED

SPECTRA OF cis,cis- AND trans,trans-1,4-DIFLUOROBUTADIENE-1-d1 AND trans,trans-

1,4-DIFLUOROBUTADIENE-1,4-d2

NORMAN C. CRAIG, YIHUI CHEN, YUHUA LU, CHRISTOPHER F. NEESE, and DEACON J. NEMCHICK, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074.

THOMAS A. BLAKE, Pacific Northwest National Laboratory, Richland, WA

99252.

Goal and Prior Knowledge • Semiexperimental (SE) structures for the nonpolar cis,cis

and trans,trans isomers of 1,4-difluorobutadiene (DFBD).• GS rotational constants for the 2-d1 isotopologues are

known.a

• GS rotational constants for the singly substituted 13C and 18F species can be predicted well from QC calculations.

• An SE structure for polar cis,trans-DFBD is known from MW spectroscopy.b

a Craig, N. C.; Easterday, C. C.; Nemchick, D. J.; Williamson, D. F. K.; Sams, R. L. J. Mol. Spectrosc. 2012, 272, 2.

b Demaison, J. F.; Craig, N. C. J. Phys. Chem. A 2011, 115, 8049.

cis,cis-DFBD-1-d1 C-type band for 19

Detail of P branch. S/N marginal. Loomis-Wood pattern recognition is essential.

Loomis-Wood Display for C-type band (19) of ccDFBD

Ka = 9, magenta; 10, red; 11, yellow; 12, green; 13, blue;

14,brown; 15, orange

Loomis-Wood Display with only RR11 highlighted

cis,cis-DFBD-1-d1 C-type bandfor 20

Rotational Constants for cis,cis-DFBD-1-d1. ground state 19(a") - C-type A/cm-1 0.4193536(8) 0.4184285(4) B/cm-1 0.0527471(15) 0.0527265(4) C/cm-1 0.0468697(10) 0.0468786(4)

J 108/cm-1 0.1042a 0.1042a

K 107/cm-1 0.2085a 0.2085a

K 106/cm-1 0.627(1) 0.618(1)

JK 107/cm-1 -0.781(5) -0.767(1)

J 108/cm-1 0.726(8) 0.7263(6) -0.96844 -0.96852 0/cm-1 867.60672(3)

s. d./cm-1 0.00039 0.00032 b/amu 2 -0.12205 -0.4044

No. trans. 1320c 1446 Ka' 5-26 5-20 Jmax 72 78

a Calculated with the B3LYP/cc-pVTZ model. b Inertial defect, = Ic - Ia

- Ib. c 862 GSCDs from 19 and 458 from 20. 0.0000015 cm-1 => 45 kHz

trans,trans-DFBD-1-d1 C-type band for 18

trans,trans-DFBD-1-d1 C-type band for 21

c for CO2

w for H2O

trans,trans-DFBD-1,4-d2 C-type band for 10

Comparison of Predicted and Observed (MW) Ground State Rotational Constants (MHz) for 13C Isotopologues of cis,trans-DFBD Obsd GS rot

consts Calcd GS rot constsa

Pred GS rot consts

% obs-pred

normal A0 12988.33256 13073.20531 B0 1467.87921 1457.26056 C0 1318.58436 1310.80715 -1-13C1 trans end A0 12936.89597 13022.62732 12938.08294 -0.0092 B0 1455.98104 1445.48111 1456.01393 -0.0023 C0 1308.45528 1300.76950 1308.48716 -0.0024 -2-13C1 A0 12987.23622 13071.93149 12987.06702 0.0013 B0 1467.15791 1456.55035 1467.16382 -0.0004 C0 1317.99827 1310.22795 1318.00173 -0.0003 -3-13C1 A0 12742.05516 12825.07159 12741.80976 0.0019 B0 1465.88139 1455.31640 1465.92089 -0.0027 C0 1314.38217 1306.68770 1314.44047 -0.0044 -4-13C1 cis end A0 12912.11123 12995.90802 12911.5371 0.0045 B0 1451.54352 1441.14312 1451.64432 -0.0069 C0 1304.61374 1296.98612 1304.68133 -0.0052

a Calculated with the MP2/cc-pVTZ model; alphas, Peter Groner's VIBROT program. b Scale factors for obs/calcd are 0.9935079 for A0, 1.0072867 for B0, and 1.0059332 for C0.

Conclusions

GS rotational constants have been obtained for the 1-d1 species of cis,cis and trans,trans-DFBD from the analysis of rotational structure in IR spectra.

GS rotational constants for the corresponding 2-d1 species were found previously.

Good GS rotational constants for singly substituted 13C and 18F species can be predicted with scaling.

The stage is set for determining semiexperimental equilibrium structures of the cis,cis and trans,trans isomers of DFBD.

Acknowledgements

Peter Groner, University of Missouri at Kansas City

Dreyfus Foundation, Senior Scientist Mentor grant.

Oberlin College, Department of Chemistry and Biochemistry.

Pacific Northwest National Laboratory, Environmental and Molecular Sciences Laboratory.