1. SUBMILLIMETER-WAVE ROTATIONAL SPECTRA OF DNC T. Amano Department of Chemistry and Department of Physics and Astronomy The University of Waterloo

2. Background  Several years ago, the dissociative recombination processes of HCNH + were investigated by observing the submm-wave lines of HCN and HNC.  Similar investigations were carried out for DCND +, DCN, and DNC.  The vibrational temperatures for the stretching vibrational modes were found to be high, in particular for ν 3 of DNC. Chemistry, Okayama University

3. HNC DNC ν 1 1300 K 1000 K ν 2 400 K 400 K ν 3 1500 K 4000 K Vibrational temperature

4. Rotational spectroscopy  Laboratory identification Creswell et al [1976], Blackman et al [1976]  Identification in interstellar space Godfrey et al [1977], Snell and Wooten [1977]  More laboratory work Okabayashi and Tanimoto [1993]; Gnd, ν 1, ν 2, ν 3 Brünken et al [2006]; ~ 2 THz, Gnd, ν 2 Bechtel et al [2006]; discharge nozzle source J = 1 – 0, 2 – 1, 3 – 2 hfs Vibrational spectroscopy Milligan, Jacox [1967]; ν 1, ν 2, ν 3 Maki, Sams [2001]; ν 1 ν 1 2787.1 cm -1 ( 2769 ) ν 2 374 ( 365 ) ν 3 1940

5.  Backward-wave oscillators ( BWO ) as radiation sources. 280 ~ 860 GHz  Extended negative glow discharge source. (Magnetic field: 160 G).  Double modulation.  CD 4 1 ~ 2 mTorr N 2 ~ 15 mTorr  Cooling the cell with liquid nitrogen  J = 5 – 4, 6 – 5, 7 – 6, 8 – 7, 9 – 8, 10 – 9, 11 – 10 Experimental Conditions

6. Overview of signals J = 9 - 8 Chemistry, Okayama University

7. v-dependence of B and D ∆B = B v-1 – B v

8. Observed frequencies for unperturbed states 1- 0 75829.460 a 38 [75350.607] b [74869.085] [73897.098] [72912.303] 2- 1 [151657.189] [150699.557] [149736.511] [147792.532] [145822.938] 3- 2 227481.655 a 11 [226045.193] [224600.621] [221684.641] [218730.233] 4- 3 303301.087 a -45 [301385.859] [299459.755] [295571.763] [291632.520] 5- 4 379114.002(5) c 4 376719.903(10) 3 374312.263(10) 7 369452.251(10) 17 [364528.129] 6- 5 454918.587(5) -1 452045.659(10) 0 449156.465(10) -3 443324.373(10) -20 437415.392(10) 7- 6 [530713.247] [527361.481] [523990.734] [517186.580] [510292.638] 8- 7 606496.297(10) -27 602665.701(10) -12 598813.390(10) -11 591037.135(10) 1 [583158.199] 9- 8 682266.161(10) -4 677956.713(10) 10 673622.816(10) 3 664874.404(15) 7 656010.396(20) -11 10- 9 758021.128(5) 9 753232.797(10) 0 748417.328(10) 9 738696.717(20) 8 728847.604(20) 13 11-10 833759.533(5) -4 828492.343(10) -2 823195.264(10) -5 812502.405(20) -8 801668.080(20) -4 Chemistry, Okayama University (001) (002) (003) (005) (007) ν/MHz Δ/kHz ν/MHz Δ/kHz ν/MHz Δ/kHz ν/MHz Δ/kHz ν/MHz Δ/kHz a Okabayashi and Tanimoto. The measurement accuracy for these lines are estimated to be 50 kHz. b Values in square brackets indicate the calculated frequencies. c Values in parentheses indicate the estimated measurement uncertainties.

9. Observed frequencies for perturbed states 1- 0 [74384.5] a [73406.&37] [72415.06] 2- 1 [148767.3] [146811.08] [144828.42] 3- 2 [223146.8] [220212.46] [217238.37] 4- 3 [297521.5] [293608.86] [289643.21] 5- 4 371889.449(10) b -57 -561 [366998.60] [362041.27] 6- 5 446249.374(10) 62 -367 440379.974(10) -28 40 434430.899(40) 29 444 7- 6 [520599.2] [513751.40] [506810.36] 8- 7 594937.510(10) 17 -129 587111.198(10) 85 135 579177.949(50) -159 -162 9- 8 669262.439(10) -36 -42 660457.986(20) 542 513 651532.619(40) 107 -68 10- 9 743572.432(10) 5 65 733787.079(20) -1618 -1814 723871.923(60) -72 -275 11-10 817865.608(10) 5 -25 807104.428(30) 1262 772 [796195.&01] Chemistry, Okayama University (004) (006) (008) J'-J'‘ obs/MHz (o-c)/kHz obs/MHz (o-c)/kHz obs/MHz (o-c)/kHz I II I II I II a Values in square brackets indicate the calculated frequencies. b Values in parentheses indicate the estimated measurement uncertainties.

10. Molecular constants for DNC in the (00v) state (000) 38152.98807(36) a 68.97119(281) a 0.1984(37) a (001) 37914.8491(13) b 68.993(19) 0.181(84) [37914.8639(44)] c [69.639(162)] c (002) 37675.4415(15) 69.037(21) 0.191(87) (003) 37434.6807(15) 69.111(21) 0.249(88) (004) 37192.3690(86) 68.242(118) (005) 36948.6873(29) 69.286(44) (006) 36703.324(115) 69.24(176) (007) 36456.2909(27) 69.560(42) (008) 36207.674(60) 71.12(94) Chemistry, Okayama University a Bechtel, Steeves, Field, Astrophys.J. 649, L53 (2006) b The values in parentheses indicate one standard errors from the least-squares fit. c Okabayashi, Tanimoto, J. Chem. Phys. 99, 3268 (1993) State B v /MHz D v /kHz H v /Hz

11. Rotational transition frequencies and molecular constants for DNC in the (100) state. 1 - 0 75704.545 a 31 2 - 1 [151407.377] b 3 - 2 227106.935 a -8 4 - 3 302801.600 a 43 5 - 4 378489.568(10) c -5 6 - 5 454169.348(10) 5 7 - 6 [529839.220] 8 - 7 605497.552(20) -7 9 - 8 681142.719(20) 4 10 - 9 756773.047(20) -2 11 - 10 832386.919(20) 1 Chemistry, Okayama University B/MHz 37852.3948(11) 37852.3907(110) D/kHz 68.761(18) 68.481(398) H/Hz 0.326(82) ----- J’ – J” ν/MHz Δ/kHz a Okabayashi, Tanimoto (1993). b Calculated frequencies. c Estimated measurement uncertainties This work OT (1993) a

12. Why is the vibrational excitation of the ν 3 mode of DNC so high?  The origin of this conspicuous excitation of the ν 3 mode of DNC is not obvious.  However, it should be closely related to mechanism of the dissociation of HCNH and DCND.  Apparently the difference in the masses of the departing H/D may be a factor causing this difference, but the vibrational temperature for ν 3 of DCN is not particularly high, about 1000 K.  When the D atom departs from the D-C side, apparently the C-N vibration is highly excited.  On the other hand, when the D-N bond is broken, not much excitation of the C-N vibration occurs. Chemistry, Okayama University

13. Conclusion  The dissociative recombination reaction of DCND + with electrons is thought to be a dominant channel to produce DNC in highly excited vibrational states; the rotational lines in levels up to (008) are observed.  The rotational and centrifugal distortion constants are determined for these states along with those for the (100) state.  The measurement accuracy is high enough to determine some higher order vibration-rotation interaction constants. Perturbed states (004), (006), (008) Tv ~ 4000 K

14. University of Waterloo Acknowledgment NSERC (Natural Science and Engineering Research Council of Canada)

15. Chemistry, Okayama University

16. Waterloo sub-mm system  Russian BWO(Backward-wave oscillator) 270-890 GHz ~1 mW stabilized, using double phase-lock loop  Double modulation technique frequency-discharge frequency-magnetic field extended negative glow discharge

17. Double modulation sub-mm system at Waterloo

18. Fundamental frequencies ( in cm -1 ) HNC ν 1 3652.7 ( Maki, Melleu 2001 ) ν 2 462.7 ν 3 2023.9 DNC ν 1 2787.1 ( Maki, Sams, 1981) ν 2 374 ( Milligan, Jacox, 1967 ) ν 3 1940 ( Milligan, Jacox, 1967 ) Chemistry, Okayama University