Millimeter-Wave Spectrum of Pyrimidine Zachary N. Heim, Brent K. Amberger, Brian J. Esselman, R. Claude Woods, Robert J. McMahon University of Wisconsin-Madison June 22, 2015

Background Equilibrium structure yet to be fully determined 2 Background Pyrimidine 0 kcal/mol (B3LYP/6-31G(d)) mB=2.28 D Equilibrium structure yet to be fully determined Not yet unambiguously identified in the interstellar medium Most stable in family of 6-member dinitrogen heterocycles Biologically relevant molecule A B C Caffeine Uracil Thymine Cytosine Pyridazine ~22.7 kcal/mol B3LYP/6-31G(d) Pyrazine ~4.1 kcal/mol B3LYP/6-31G(d) B. J. Esselman, B. K. Amberger, J. D. Shutter, M. A. Daane, J. F. Stanton, R. C. Woods, and R. J. McMahon, “Rotational spectroscopy of pyridazine and its isotopologs from 235-360 GHz: Equilibrium structure and vibrational satellites,” J. Chem. Phys. 139, 224304 (2013); doi: 10.1063/1.4832899. Z. Kisiel, L. Pszczolkowski, I. R. Medvedev, M. Winnewisser, F. C. De Lucia, E. Herbst, J. Mol. Spectrosc. 233, 231-243 (2005). G. L. Blackman, R. D. Brown, F. R. Burden, J. Mol. Spectrosc. 35, 444-454 (1970). W. Caminati, D. Damiani, Chem. Phys. Lett. 179, 460-462 (1991). Charnley, S., Ehrenfreund, P., & Kuan, Y.-J. 2001, Spectrochim. Acta A, 57, 685

The Instrument and Experiment 3 The Instrument and Experiment Produce tone-burst modulated radiation up to 360 GHz (nominally 270-360 GHz) 10 cm diameter by 3m long absorption cell Controlled by software made in LabVIEW2010 Commercially available sample Room Temperature (298 K)

Initial Spectrum Collected 4 Initial Spectrum Collected 13C and 15N Isotopologues Main Isotopologue

5 Main Isotopologue 29 28 27 26 26 30 32 34 36 38 40 42 J’=44 ν11 = 391.3 cm-1 29 28 27 26 26 30 32 34 36 38 40 42 J’=44 ν16 = 342.6 cm-1 J’=57 55 53 51 49 47 45 Q-branch, ν0 R-branch, ν0 J’=44 J’=44 32 32 30 28 26

Experimental and Computational Alphas 6 Experimental and Computational Alphas Mode Frequency (cm-1) aA (MHz) Comp aB (MHz) aC (MHz) Exp Nlines sfit n16 342.63 -5.977 0.740 3.820 -5.953 0.685 3.897 1754 0.0303 n11 391.28 -2.403 -5.084 3.072 -2.448 -5.151 3.127 1679 0.0302 n24 619.04 3.803 -5.507 -9.389 3.766 -6.136 -9.598 363 0.0249 Calculated with an anharmonic frequency VPT2 calculation at CCSD(T)/ANO1

Complications of Turnarounds 7 Complications of Turnarounds J’=57 56 55 54 53 48 49 50 51 52 45 46 47 44 43 42 41 40

Main Isotopologue13C and 15N Isotopologues Sextic S-reduced Hamiltonian Representation IIIr 8 C4H4N2 [2-13C] [4-13C] [5-13C] [1-15N] A0 (MHz) 6276.82717 (21) 6152.67912 (47) 6256.09754 (20) 6132.81825 (31) 6253.95862 (46) B0 (MHz) 6067.16469 (23) 6067.53971 (44) 5957.21874 (20) 6067.35941 (27) 5954.15093 (51) C0 (MHz) 3084.44822 (34) 3054.25189 (60) 3050.84589 (27) 3049.30527 (19) 3049.53055 (71) DJ (kHz) 1.47123(20) 1.44438(39) 1.44256(12) 1.442778(92) 1.44275(37) DJK (kHz) -2.452591(34) -2.40564(76) -2.40137(19) -2.40248(26) -2.40552(79) DK (kHz) 1.104892(68) 1.08351(43) 1.08143(14) 1.08196(18) 1.08408(53) d1 (kHz) 0.011517(42) 0.02084(14) 0.001471(61) 0.02183(16) 0.00144(13) d2 (kHz) 0.022030(71) 0.018261(41) 0.013894(29) 0.018304(40) 0.013904(58) HJ (Hz) 0.000392(52) 0.00064(11) 0.000792(23) [0] 0.000535(95) HJK (Hz) -0.0027287(82) -0.00214(29) -0.002798(28) -0.002991(99) HKJ (Hz) 0.003362(13) 0.00291(35) 0.003679(39) 0.00290(24) HK (Hz) -0.001348(12) -0.00132(15) -0.001601(29) -0.00059(21) h1 (Hz) 0.000019(14) h2 (Hz) -0.000154(53) h3 (Hz) 0.000039(13) Nlines 1454 266 604 211 281 σfit 0.0291 0.0383 0.0355 0.0398 0.0393

Main Isotopologue and 13C and 15N Isotopologues 9 Main Isotopologue and 13C and 15N Isotopologues C4H4N2 [2-13C] [4-13C] [5-13C] [1-15N] A0 (MHz) 6276.82717 (21) 6152.67912 (47) 6256.09754 (20) 6132.81825 (31) 6253.95862 (46) B0 (MHz) 6067.16469 (23) 6067.53971 (44) 5957.21874 (20) 6067.35941 (27) 5954.15093 (51) C0 (MHz) 3084.44822 (34) 3054.25189 (60) 3050.84589 (27) 3049.30527 (19) 3049.53055 (71) Nlines 1454 266 604 211 281 σfit 0.0291 0.0383 0.0355 0.0398 0.0393

Synthesis of Deuterium Enriched Samples 10 Sample of pyrimidine in LiOtBu/tBuOD buffer Heated to 125oC for 58 hours Purified via silica gel column and freeze/pump/thawing

Deuterated Isotopologues 11 Deuterated Isotopologues 7.1 9.3 1.2 1.0 2.9 ? ? 3.1 8.4

Dipole Components Isotopologue mA (D) mB (D) C4H4N2 2.28 [2,4-2H] 1.50 12 Dipole Components A Isotopologue mA (D) mB (D) C4H4N2 2.28 [2,4-2H] 1.50 1.72 [2-13C] [2,5-2H] [4-13C] 0.42 2.24 [4,5-2H] 1.55 1.67 [5-13C] [4,6-2H] [1-15N] 0.44 [2,4,6-2H] 2.13 0.82 [2-2H] [4-2H] 0.74 2.16 [4,5,6-2H] [5-2H] [2,4,5,6-2H] 4 2 B C4H4N2 6 A 4 2 B 5 [4,5-2H] 6

Quartets in the [4,5-2H] Spectrum 13 Quartets in the [4,5-2H] Spectrum b-type 2819,10⇦ 2718,9 b-type 2818,10⇦ 2719,9 a-type 2819,10⇦ 2719,9 a-type 2818,10⇦ 2718,9

Deuterium Substituted Isotopologues Sextic S-reduced Hamiltonian in Representation IIIr 14 [2-2H] [4-2H] [5-2H] [2,4-2H] [4,5-2H] [4,6-2H] [4,5,6-2H] A0 (MHz) 6066.842 (37) 6242.39763 (21) 6066.96119 (42) 5934.853 (11) 5913.94866 (97) 6082.41741 (33) 5680.01271 (38) B0 (MHz) 5871.764 (39) 5694.50606 (18) 5840.14916 (45) 5604.080 (11) 5602.3946 (16) 5457.75984 (35) 5457.63939 (40) C0 (MHz) 2983.30038 (84) 2977.37741 (20) 2975.12047 (30) 2881.89426 (41) 2876.48892 (64) 2876.11603 (14) 2782.89178 (47) DJ (kHz) 1.3454(74) 1.333718(96) 1.33773(17) 1.2065(39) 1.21212(57) 1.20830(16) 1.10018(23) DJK (kHz) -2.2324(84) -2.20856(14) -2.22021(28) -2.0004(47) -2.0063(14) -1.99430(37) -1.81944(60) DK (kHz) 1.0007(16) 0.989004(97) 0.99654(17) 0.89821(89) 0.89882(78) 0.89067(22) 0.81554(38) d1 (kHz) -0.13(10) -0.044650(79) -0.06386(53) -0.001(29) -0.03692(73) -0.04145(11) 0.00369(13) d2 (kHz) -0.24(21) -0.007145(73) 0.008069(18) 0.023(38) -0.01177(23) 0.020398(39) 0.011864(61) HJ (Hz) [0] 0.000577(17) 0.000525(64) HJK (Hz) -0.002253(24) -0.00209(13) HKJ (Hz) 0.002843(37) 0.00263(13) HK (Hz) -0.001163(24) -0.001028(61) h1 (Hz) -0.00041(35) h2 (Hz) -0.000146(63) h3 (Hz) Nlines 108 913 586 202 177 422 195 σfit 0.0425 0.0373 0.0365 0.0390 0.0278 0.0346 0.0299

Deuterium Substituted Isotopologues 15 Deuterium Substituted Isotopologues [2-2H] [4-2H] [5-2H] [2,4-2H] [4,5-2H] [4,6-2H] [4,5,6-2H] A0 (MHz) 6066.842 (37) 6242.39763 (21) 6066.96119 (42) 5934.853 (11) 5913.94866 (97) 6082.41741 (33) 5680.01271 (38) B0 (MHz) 5871.764 (39) 5694.50606 (18) 5840.14916 (45) 5604.080 (11) 5602.3946 (16) 5457.75984 (35) 5457.63939 (40) C0 (MHz) 2983.30038 (84) 2977.37741 (20) 2975.12047 (30) 2881.89426 (41) 2876.48892 (64) 2876.11603 (14) 2782.89178 (47) Nlines 108 913 586 202 177 422 195 σfit 0.0425 0.0373 0.0365 0.0390 0.0278 0.0346 0.0299

Equilibrium Structure Calculation 16 Equilibrium Structure Calculation A0, B0, C0 taken from fits and converted to determinable form A0”, B0”, C0” Vibration-rotation and electron mass corrections added Distance and angle parameters least squares fit Vibration-rotation corrections calculated with an anharmonic frequency VPT2 calculation at the CCSD(T)/ANO1 level. Electronic corrections calculated at the CCSD(T)/ANO1 level

Calculated and Experimental Equilibrium Structures 17 Calculated and Experimental Equilibrium Structures Bond Lengths And Angles Experimental Re (Å) CCSD(T)/ANO1 Re (Å) RC(2)-N(3) 1.3346(9) 1.340 RN(3)-C(4) 1.3366(8) 1.341 RC(4)-C(5) 1.3834(6) 1.392 RC(2)-H 1.0813(9) 1.084 RC(4)-H 1.0830(7) 1.085 RC(5)-H 1.0812(8) 1.081 θC(2)-N(3)-C(4) 115.52(6) 115.386 θN(3)-C(4)-C(5) 122.35(5) 122.456 θC(4)-C(5)-C(6) 116.85(5) 116.609 θN(1)-C(2)-H 116.29(6) 116.146 θC(4)-C(5)-H 121.58(5) 121.696 θC(5)-C(4)-H 121.46(9) 121.171 RC(4)-H RC(2)-N(3) RN(3)-C(4) RC(5)-H RC(4)-C(5) RC(2)-H θC(5)-C(4)-H θC(4)-C(5)-H θN(1)-C(2)-H θC(2)-N(3)-C(4) θN(3)-C(4)-C(5) θC(4)-C(5)-C(6)

Importance of Corrections 18 Importance of Corrections Isotopologue Di (mÅ2) a corrected a and e- corrected C4H4N2 0.0350 -0.0132 -0.000797 [2-13C]-C4H4N2 0.0352 -0.0135 -0.000609 [4-13C]-C4H4N2 0.0355 -0.0137 -0.000944 [5-13C]-C4H4N2 0.0360 -0.0116 0.000481 [1-15N]-C4H4N2 0.0356 -0.0131 -0.000395 [2-2H]-C4H4N2 0.0308 -0.0140 -0.000164 [4-2H]-C4H4N2 0.0318 -0.0136 0.0000361 [5-2H]-C4H4N2 0.0329 -0.0134 -0.000103 [2,4-2H]-C4H4N2 0.0285 0.000719 [4,5-2H]-C4H4N2 0.0299 0.000865 [4,6-2H]-C4H4N2 0.0275 -0.0149 0.000924 [4,5,6-2H]-C4H4N2 0.0269 0.00167 Vibration-rotation corrections calculated with an anharmonic frequency VPT2 calculation at the CCSD(T)/ANO1 level. Electronic corrections calculated at the CCSD(T)/ANO1 level

Comparison to Other Structures 19 Comparison to Other Structures Experimental Computational Parameters Re (Å) CCSD(T)/ANO1 Substitution Rs (Å) Kisiel et al. Piccardo et al. Rese (Å) RC(2)-N(3) 1.3346(9) 1.340 1.338 1.337(2) 1.3334(1) RN(3)-C(4) 1.3366(8) 1.341 1.344 1.332(3) 1.3355(1) RC(4)-C(5) 1.3834(6) 1.392 1.393 1.393(2) 1.3867(3) RC(2)-H 1.0813(9) 1.084 1.087 - [1.0822] RC(4)-H 1.0830(7) 1.085 1.086 [1.0826] RC(5)-H 1.0812(8) 1.081 1.082 [1.0795] θC(2)-N(3)-C(4) 115.52(6) 115.386 115.80 115.8(3) 115.69(1) θN(3)-C(4)-C(5) 122.35(5) 122.456 122.38 122.4(3) 122.27(2) θC(4)-C(5)-C(6) 116.85(5) 116.609 116.42 116.4(2) 116.72(1) θN(1)-C(2)-H 116.29(6) 116.146 116.39 116.31(1) θC(4)-C(5)-H 121.58(5) 121.696 121.79 121.64(1) θC(5)-C(4)-H 121.46(9) 121.171 120.96 [121.36] Z. Kisiel, L. Pszczolkowski, I. R. Medvedev, M. Winnewisser, F. C. De Lucia, E. Herbst, J. Mol. Spectrosc. 233, 231-243 (2005). M. Piccardo, E. Penocchino, C. Puzzarini, M. Biczysko, V. Barone, J. Phys. Chem. 119, 2058-2082 (2015).

Thanks! The McMahon-Woods Research Group 20 Robert J. McMahon R. Claude Woods 8:30 Friday in 217 Noyes Lab (FE01) Brian J. Esselman Brent K. Amberger 8:47 Friday in 217 Noyes Lab (FE02) Ben C. Haenni Stephanie N. Knezz 5:00 Thursday in 217 Noyes Lab (RJ13) Nick A. Walters 10:12 Friday in 217 Noyes Lab (FE06) Vanessa L. Orr Cara E. Schwarz Next! Maria A. Zdanovskaia P. Matisha Kirkconnell