1. THE MICROWAVE SPECTRA OF THE LINEAR OC HCCCN, OC DCCCN, AND THE T-SHAPED HCCCN CO 2 COMPLEXES The 62 nd. International Symposium on Molecular Spectroscopy, RG 09 LU KANG Department of Natural Sciences, Union College, Barbourville, KY 40906 STEWART E. NOVICK Department of Chemistry, Wesleyan University, Middletown, CT 06459

2. General Introduction IR study of the OC---HCCCN, and the HCCCN---CO 2 X. Yang, R.Z. Pearson, G. Scoles; Chem. Phys. Lett., 204(12), p145, 1993 X. Yang, R.Z. Pearson, and G. Scoles; J. Mol. Spectrosc., 180(1), p1, 1996 Rotational spectroscopy study of the OC---HCN E. J. Goodwin, A. C. Legon; Chem. Phys., 87, p81, 1984 Both Linear and T-shaped HCN---CO 2 exist T. D. Klots, R. S. Ruoff, H. S. Gutowsky; J. Chem. Phys., 90(8), p4216, 1989 K. R. Leopold, G. T. Fraser, W. Klemperer; J. Chem. Phys., 80(3), p1039, 1984 Complete rotational spectroscopy investigations of the weakly bound Ng---HCCCN van der Waals complexes He---HCCCN: W. C. Topic, W. Yäger; J. Chem. Phys.,123(6), p064303/1, 2005 Ne---HCCCN: A. Huckauf, W. Yäger; manuscript in preparation. Ar---HCCCN: A. Huckauf, W. Yäger, P. Botschwina, R. Oswald; J. Chem. Phys., 119(15), p7749, 2003 Thorough understanding of the subunits: CO and HCCCN CO: F. J. Lovas, P. H. Krupenie; J. Phys. Chem. Ref. Data, 3(1), p245, 1974 HCCCN: W. J. Lafferty, F. J. Lovas; J. Phys. Chem. Ref. Data, 7(2), p441, 1978

3. Experiment Balle-Flygare Type Fourier transform microwave spectrometer (FTMW) at Wesleyan University  Molecular beam pulsed-nozzle (~3 K)  Cover 3.7 – 26.5 GHz  ~ 1 kHz frequency resolution The synthesis of Ethyl cyanide (Cyanoacetylene), HCCCN.  C. Moureu, J. C. Bongrand; Ann. Chim. (Paris), 14, p47, 1920.  Propiolamide is commercially available (Acme Bioscience Inc.)  Deuterated sample, DCCCN was also made! 0.5% HCCCN (DCCCN) + 7.5% CO / Ar or Ne carrier gas 0.5% HCCCN (DCCCN) + 10% CO 2 / Ar or Ne carrier gas

4. Spectrum

6. Hamiltonian H = H R + H Q H R : the effective Hamiltonian for the vibrational ground state semi-rigid linear molecules H R = B 0 J 2 – D 0 J 4 + H 0 J 6 E J = B 0 J(J+1) – D 0 J 2 (J+1) 2 + H 0 J 3 (J+1) 3 J+1→J = 2B 0 (J+1) – 4D 0 (J+1) 3 + H 0 (J+1) 3 [(J+2) 3 -J 3 ] H Q : the nuclear quadrupole coupling interactions between the molecular rotation angular momentum, J, and the nuclear spin angular momentum, I. H Q = The nuclear spin of Nitrogen atom is1, hence, J + I (N) = F

7. Spectroscopic constants

9. Spectroscopic constants of HCCCN---CO 2 The observed spectra agree with the T-shaped structure. IR spectroscopy determined rotational constants: B” = 0.0254463(59) cm -1 i.e., 762.9(19) MHz C” = 0.0254463(59) cm -1 i.e., 715.5(18) MHz X. Yang, R. Z. Pearson, G. Scoles; J. mol. Spectro.180, p 1-6, 1996 The obtained rotational constants from the microwave spectroscopy are in good agreement with the IR values.

10. Structural Analysis: Linear Model IR spectroscopy determined r OC-HC = 2.615Å for OC---HCCCN complex Yang, et. al., Chem. Phys. Lett., 204(12), p145-151, 1993. Microwave spectroscopy determined r OC-HC = 2.577Å for OC---HCN Goodwin, et. al., Chem. Phys., 87, p81-92, 1984.

11. Structural Analysis: Linear Model How to find a distance that can best descrbe the complex?

12. Structural Analysis: Procession Model The description of the procession model: E. J. Goodwin & A. C. Legon; Chem. Phys., 87, p81 – 92, 1984

13. Structural Analysis: Procession Model Average effect of the procession around the a-axis The geometry of the complex is determined by r c.m. and θ, , µ, can be obtained from the experiment.  can be obtained from the quadrupole coupling constant of 14 N

14. Structural Analysis: Procession Model For example, OC---HCCCN,  aa ( 14 N)=-4.20865(55)MHz, and the  0 ( 14 N) for free HCCCN is:  0 ( 14 N)=-4.31806(38)MHz, then: OC---HCCCN:  =7.468(1)  For other isotopomers: OC---DCCCN:  =7.31(4)  18 OC---HCCCN:  =7.432(3)  18 OC---DCCCN: N/A O 13 C---HCCCN:  =7.473(1)  O 13 C---DCCCN:  =14.17(2)  OC---H 13 CCCN:  =7.341(3)  OC---D 13 CCCN: N/A OC---HC 13 CCN:  =7.473(1)  OC---DC 13 CCN:  =6.05(6)  OC---HCC 13 CN:  =7.435(1)  OC---DCC 13 CN:  =9.89(3)  OC---HCCC 15 N: N/AOC---DCCC 15 N: N/A   = 7.44(5)  ↔   OC---HCN = 13-14 

15. Structural Analysis: Procession Model I bb is determined by the (θ,  r 2 c.m.  ½ ) pair, how do we estimate θ? Note that r c-c is almost isotropically invariant, and, (θ, r c-c ) can also be used to determine I bb, i.e., I b exp Construct a set of (θ, r c-c ) pairs from the main isotopomer and use them to reproduce I bb s for other isotopomers, and find the best matched (θ, r c-c ) pair to get the answer. Examples: 18 OC---HCCCN: O 13 C---HCCCN: comparing with 18 OC---HCN:  ~ 15º O 13 C---HCN:  ~ 10º The procession model does not work very well for HCCCN isotopomers!  ~ 0º - 90º (similar to the OC---HCN when use this model to handle HCN isotopomers!)

16. Conclusion 1. The rotational spectra of the weakly bound van der Waals complex dimers, including, OC---HCCCN, OC--- DCCCN, and HCCCN---CO 2 are observed. 2. All 13 C (1.07%), 15 N (0.37%), and 18 O (0.205%) isotopomers are found in natural abundance! 3. The obtained results are in good agreement with previous studies 4. OC---HCCCN / OC---DCCCN is linear shaped. The procession model is effective to describe this system. 5. The T-shaped HCCCN---CO 2 has been observed. We tried, but the linear shaped CO 2 ---HCCCN was not found yet! 6. Why the procession model failed to reproduce the geometry of the OC---HCCCN complex when the HCCCN subunit is substituted by 13 C or 15 N isotopes?

17. Future Plan 1. Try to improve the quality of the data for OC---DCCCN by observing low frequency transitions. (get the eqQ for D). 2. Try to get the nuclear quadrupole coupling splittings due to the 13 C of O 13 C-HCCCN. (can help us figure out  very accurately) 3. Keep searching for the linear shaped CO 2 ---HCCCN dimer. 4. We already observed N 2 ---HCCCN. 5. We already observed HCCCN---HCCCN, HCCCN---DCCCN, DCCCN---HCCCN, and DCCCN---DCCCN dimers (The low frequency data will really help!). 6. Searching for NO---HCCCN complex.

18. Acknowledgement Andrea Meini Department of Chemistry, Wesleyan University Dr. Steven Shipman, Justin Neill, University of Virginia Professor Wallace Pringle Department of Chemistry, Wesleyan University Union College, and Professor Brooks Pate, University of Virginia.