SUBMILLIMETER-WAVE ROTATIONAL SUBMILLIMETER-WAVE ROTATIONAL SPECTRA OF DNCSPECTRA OF DNC

T. Amano

Department of Chemistry

and

Department of Physics and Astronomy

The University of Waterloo

BackgroundBackground

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 ν3 of DNC.

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HNC DNC

ν1 1300 K 1000 K

ν2 400 K 400 K

ν3 1500 K 4000 K

Vibrational temperature

Rotational spectroscopyRotational 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, ν1, ν2, ν3

Brünken et al [2006]; ~ 2 THz, Gnd, ν2

Bechtel et al [2006]; discharge nozzle source

J = 1 – 0, 2 – 1 , 3 – 2 hfs

Vibrational spectroscopyVibrational spectroscopy

Milligan, Jacox [1967]; ν1 , ν2, ν3

Maki, Sams [2001]; ν1

ν1 2787.1 cm-1 ( 2769 ) ν2 374 ( 365 ) ν3 1940

Backward-wave oscillators ( BWO ) as radiation sources. 280 ~ 860 GHz Extended negative glow discharge source.

(Magnetic field: 160 G). Double modulation. CD4 1 ~ 2 mTorr

N2 ~ 15 mTorr Cooling the cell with liquid nitrogen J = 5 – 4, 6 – 5, 7 – 6, 8 – 7, 9 – 8, 10 – 9, 11 – 10

Experimental ConditionsExperimental Conditions

Overview of signalsOverview of signalsJJ = 9 - 8 = 9 - 8

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v-dependence of v-dependence of BB and and DD

∆B = Bv-1 – Bv

Observed frequencies for unperturbed statesObserved frequencies for unperturbed states

1- 0 75829.460a 38 [75350.607]b [74869.085] [73897.098] [72912.303]

2- 1 [151657.189] [150699.557] [149736.511] [147792.532] [145822.938]

3- 2 227481.655a 11 [226045.193] [224600.621] [221684.641] [218730.233]

4- 3 303301.087a -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

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(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.

Observed frequencies for perturbed statesObserved 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]

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(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.

Molecular constants for DNC in the (00v) stateMolecular 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)

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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 Bv/MHz Dv/kHz Hv/Hz

Rotational transition frequencies and molecular Rotational transition frequencies and molecular constants for DNC in the (100) state.constants for DNC in the (100) state.

1 - 0 75704.545a 31

2 - 1 [151407.377]b

3 - 2 227106.935a -8

4 - 3 302801.600a 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

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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

Why is the vibrational excitation of the Why is the vibrational excitation of the νν33 mode mode

of DNC so high?of DNC so high?

The origin of this conspicuous excitation of the ν3 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 ν3 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.

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ConclusionConclusion

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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

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Acknowledgment

NSERC (Natural Science and Engineering Research Council of Canada)

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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

Double modulation sub-mm system at Waterloo

Fundamental frequencies ( in cmFundamental frequencies ( in cm-1-1 ) )

HNC

ν1 3652.7 ( Maki, Melleu 2001 )

ν2 462.7

ν3 2023.9

DNC

ν1 2787.1 ( Maki, Sams, 1981)

ν2 374 ( Milligan, Jacox, 1967 )

ν3 1940 ( Milligan, Jacox , 1967 )

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