1. Terahertz spectroscopy of molecules, radiacls and ions using Evenson-type tunable FIR spectrometer Fusakazu Matsushima Department of Physics, University of Toyama, Japan 67 th Columbus meeting, June 20, 2012

2. Scope of this talk “Evenson-type” = difference frequency of CO 2 laser lines = TuFIR spectrometer 1. Property of the spectrometer (Review) Tunability, accuracy, sensitivity Trial to extend the properties 2. Examples (mainly of ions) Glow discharge cell Molecular cation (HeH +, H 2 D + ) Molecular anion (OH - ) Extended negative glow discharge cell Temperature ( N 2 H + ) Recent work (H 2 F + )

3. Ken. M. Evenson NIST (Boulder, Colorado) Time & Frequency Division

4. late Ken. M. Evenson NIST (Boulder, Colorado) Time & Frequency Division in 1993 at Toyama

5. His wife called him “a man of curiosity”

6. “The final measurement of speed of light” Talk in Toyama (1993)

7. MIM diode as detector / mixer Chain for the measurement of CO 2 laser frequency Standard: Cs atomic clock MIM diode whisker

8. CO 2 laser lines 10P 10R 9P 9R angle of grating output power 1. Frequency range

9. Distribution of CO 2 laser lines

10. TuFIR (CO 2 laser difference frequency) How to obtain the tunability using wave guide CO 2 laserusing MW source tunability ~ 100MHz need many combinations tunability ~ 20GHz power: 2 nd > 3 rd

11. Evenson-type TuFIR in the world of 1990s NIST (Corolado): 2 nd, 3 rd Minnesota (K.R. Leopold): (2 nd ?), 3 rd LENS(M. Inguscio, Firenze, Italy): 3 rd Toyama: 3 rd (2 nd prepared) NIST 2 nd order system

12. TuFIR spectrometer FIR =| I - II |± MW

13. MIM diode micro wave whisker roof top mirror base FIR CO 2 laser

14. Properties 1. Frequency Range 2. Precision 3. Sensitivity ( Power of the radiation source)

15. Distribution of CO 2 laser lines ≈ 5.5THz

16. upper or lower sideband difference freq. of two CO 2 lasers Fourier transform spectrometer TuFIR

17. CO 2 fluorescence cell Laser frequency (cavity length) 4.3  m fluorescence 1st derivative Stabilization of the CO 2 laser frequency Accuracy of laser frequency table <2kHz Accuracy of laser stabilization one CO 2 laser 25kHz → difference freq. 36 kHz 2. Precision

18. NH 3 s(J=7,K= ３ ) ← a(J=6,K= ３ ) 4126502.4414126477.036(37)4126452.441 Frequency(MHz) 9P(20)-10R(24) = 4138411.441 (MHz) MW =11909 ～ 11959 （ MH ｚ） Fitting with Voigt profile ⇒ center frequency

19. ← Bolometer Synthesized source power ( 3 rd order TuFIR spectometer) characteristics of the components in the detector frequency characteristics of MIM diode 3. Sensitivity (Power of the source)

20. property of TuFIR spectrometer 1. frequency range about 30 GHz ~ 5.5 THz (or 6THz, 10THz) 2. measurement accuracy of spectral line several tens kHz for strong (neutral) molecules several hundres kHz for weak (ionic) molecules 3. power of the synthesized FIR several tens of nW ~ several hundreds of nW

21. Trials for extending the properties 1. Frequency range ⇒ higher order nonlinearity of MIM ⇒ use of NH 3 laser 2. Resolution ⇒ sample in a molecular beam

22. ｜ ν I ー ν II ｜  ν MW = 2.4THz 9P(14)-10R(14) 2.4THz ｜ ν I ー ν II ｜  2  ν MW = 2.4THz 10R(34)-10P(20) 1.2THz 1. Multiple of IR frequency 3 wave mix 5 wave mix H 2 18 O 3 21 ← 3 12

23. up to 9.1THz CO 2 laser + NH 3 laser H. Odashima, L.R. Zink, & K.M. Evenson, Opt. Lett. vol.24, 406 (1999) CH 3 OH (n=1,K=7,J=19)←(0,6,19) A-type transition Maximum record of TuFIR

24. Effusive molecular beam Multi channel array (diam 10μm, length 2mm) Optical Path length: about 30 cm Stagnation pressure: 0.15 Torr effective sample pressure ≤ 1mTorr 2. Molecular beam

25. bulk gas 2x10 -4 Torr beam width= 220kHz (peak to peak) H 2 18 O 4 32 ← 4 23

26. Molecules and ions measured with TuFIR spectrometer in Toyama (1) neutral molecules, radicals LiH, KH, １８ OH, NH, NH 3 H 2 O ( H 2 16 O, H 2 17 O, H 2 18 O, D 2 O, and H 2 16 O (v 2 =1 excited state)) (2) molecules with internal rotation CH 3 OH (3) cation protonated rare gas atoms (HeH + ， NeH + ， ArH + ， KrH + ， XeH + ， including their isotopic species) H 2 D +, N 2 H +, H 2 F + (4) anion OH - ， OD - Part 2.

27. Discharge cell 1. Glow discharge cell dc discharge ac discharge: velocity modulation technique Molecular cation (HeH +, H 2 D + ) Molecular anion (OH - ) 2. Extended negative glow discharge cell dc discharge Temperature ( N 2 H + ) Recent work (H 2 F + ) collaboration: T. Amano (U. Waterloo) K.Kawaguchi (Okayama U.) R,Fujimori (Okayama U.) (collaboration with Prof. Amano (Waterloo, Canada))

28. Fig.1 TuFIR 分光計 Velocity modulation: detects ions only Configuration for detecting ionic species

29. HeH + J=1  0 The lowest frequency rotational line 2010.1839 (2) GHz HeH +

30. Dunham coefficient Y kl E vJ = Σ Y kl (v+ 1/2 ) k [J(J+1)] l ( a set of coefficientsY kl for each isotope) To calculate all the isotopes with a set of coefficients U kl Y kl ＝ μ -(k/2+l) U kl Reduced mass μis not enough to fit all the isotopes. Y kl ＝ μ -(k/2+l) U kl [1+m e Δ He kl / M He + m e Δ H kl /M H ] Correction terms usingΔvalues are necessary. Breakdown of Born-Oppenheimer approximation.

31. HeH + Rotational Transition transition frequencyobs-calc 4 HeH + J=1  02010183.873 (202) 0.108 J=2  14008733.084 (194)-0.148 4 HeD + J=2  12434626.571 (143) 0.077 J=3  23641427.274 (384)-0.210 J=4  34835691.417 (166) 0.039 3 HeH + J=1  02139522.472 (300)-0.213 J=2  14265839.060 (300) 0.330 3 HeD + J=2  12696099.975 (255)-0.021 J=3  24031223.001 (511)-0.650 HeH +

32. HeH + : 3 HeH +, 4 HeH +, 3 HeD +, 4 HeD + NeH + : 20 NeH+, 20 NeH+, 22 NeD+, 22 NeD+ ArD + : KrH + : 82 KrD +, 84 KrD +, 8 6KrD +, 82 KrH + XeH + : isotopes of 124 Xe, 126 Xe, 128 Xe, 129 Xe, 130 Xe, 131 Xe, 132 Xe, 134 Xe, 136 Xe, and H, D protonated rare gas atoms

33. typical trace of H 2 D + 2 11  1 10 H2D+

35. 3363550.541 frequency （ MHz ） 3363658.541 intensity(arb. units) OH - transition frequency (MHz) J=4  3 4478174.516 (387) J=3  2 3363607.066 (238) J=2  1 2244776.819 (240) J=1  0 1123100.985 (324)

36. OD - J=2←1 J=3←2 J=5←4 J=6←5 J=8←7 Intensity (arb.units) D 2 O/O 2 =54.5/5Pa,AC1.2kHz,1.1A,4.8kV,Scan6 回, エタノール冷却 2 ℃, 湿度 60%,FIR200mV( ≒ 100nW) ND 3 /O 2 =35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回, 水冷, 湿度 29%,FIR140mV( ≒ 70nW) ND 3 /O 2 =35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回, 水冷, 湿度 26%,FIR160mV( ≒ 80nW) D 2 O/O 2 =23.5/5Pa,AC1.2kHz,1.2A,4.5kV,Scan3 回, 水冷（溜め置き）, 湿度 60%,FIR150mV( ≒ 75nW) ND 3 /O 2 =35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回, 水冷, 湿度 24%,FIR40mV( ≒ 20nW) Fit 1196791.042(0.486)MHz

37. OH -, OD -

38. Extended negative glow discharge cell Compared to "normal" glow discharge cell: Gas pressure : smaller by 1 or 2 orders of magnitude ⇒ small consumption of gases Electric current: smaller by 1 or 2 orders of magnitude ⇒ Discharge noise does not destroy MIM contact !!

39. N 2 H + J=14 ← 13 E" = 283 cm -1 N 2 :H 2 :Ar=0.9 ; 0.9 : 2Pa 7mA, 1.7kV

40. J=14 ← 13(E" = 283 cm -1 ) J=16 ← 15(E" = 373 cm -1 ) J=17 ← 16(E" = 422 cm -1 ) J=9 ← 8(E" = 112 cm -1 ) (E" = 140 cm -1 )J=10 ← 9

41. Intensity of the spectral line E” : lower energy level of the absorption T : rotational temperature ln{Si/(J+1)} = -(1/kT)E” + const. slope ⇒ T

42. T = 129K

43. Extended Negative Glow Discharge discharge : 10 mA, 4 kV gas pressure ≈ 2 Pa (buffer) → mean free path comparable to the cell dimension → cold buffer gas cool down the ion ? "Normal" Glow Discharge discharge : 500 mA, 4kV gas pressure ≈ 40 Pa how to overcome : liq. nitrogen cooling → water cooling Trot ≈ 500 KTrot ≈ 130 K

44. N 2 H + J=14 ← 13 E" = 283 cm -1 Lig. Nitrogen cooling

45. Water cooling nothing !

46. N 2 H + J=5←4 temperature dependence, sub-mm spectrometer (by Amano) -200C (liq. N2 temp) -100 -85 -65 -30 -15 -5 +20 (room temp.)

47. H2F+H2F+ ⇒ H 2 F + in space? Fluorine contained species detected in space. ( interstellar space, circumstellar envelopes) AlF, HF, CF+ H 2 Cl + was detected with Herschel HIFI. (NGC6334I, Sgr B2 ) (D. C. Lis et al. A&A 521, L9(2010)) Cosmic abundance of F ~ abundance of Cl

48. Previous laboratory measurements for H 2 F + IR Laser spectroscopy with velocity modulation technique Schäfer and Saykally, J. Chem. Phys. 81, 4189 (1984) ~ 3 µm region, ν 1 and ν 3 bands FTIR Fujimori, Hirata, Kawaguchi, and Morino, International Symposium on Molecular Spectroscopy (Columbus, OH), 2010. ν 2 band in addition to ν 1 and ν 3 bands sub-mm BWO (Univ. Waterloo) with extended negative glow discharge cell R. Fujimori, K. Kawaguchi, and T. Amano, Ap. J. Lett. 729, L2 (2011) 473-774GHz, 5 pure rotational lines

49. Astrophys. J. Lett., 729 L2 (2011)

50. Length: ~ 1.3m Voltage: 2 ~ 3kV Current: ~10mA T: 0 ~ -70 C HF : H2 : Ar = 0.2 : 1 : 2Pa Extended negative glow discharge cell with ethanol cooling HF heat cell: prepared by Fujimori & Kawaguchi

52. H 2 F + 3 03 ← 2 12 T= -70C

53. H 2 F + 1 11 ←0 00 1305306.600 (56) MHz

54. H 2 F + 1 11 -0 00 1305306.503 (073) MHz 3 03 -2 12 1370911.418 (048) 4 13 -4 04 1425857.036 (059) 5 23 -5 14 1737165.499 (066) 4 22 -4 13 1748037.582 (085) 3 21 -3 12 1823629.057 (070) 2 12 -1 01 1850081.989 (050) H 2 F + : isoelectronic to H 2 O, mass close to H 2 18 O

55. red arrow: TuFIR

56. Lowest frequency rotational lines para 1 11 -0 00 1305306.503 (73) MHz (TuFIR measurement, Toyama) ortho 1 10 -1 01 760928.937 (10) MHz (sub-mm measurement, Waterloo)

57. liq. N 2 cell without glass-blowing

58. Collaboration Univ. of Toyama K. Takagi (prof. emeritus) H. Odashima (now in Meiji univ. in Tokyo) Y. Moriwaki K. Kobayashi many students including T. Yonezu (now in Nobeyama Radio Obs.) T. Oka (Chicago Univ.) --- start of studies of ionic species T.Amano (Univ. Waterloo, Canada) --- ext. neg. glow discharge cell and works using it K.Kawaguchi (Okayama Univ.) late J.M. Brown (Oxford Univ.) and of course late K.M. Evenson (NIST Boulder Colorado)

59. Thank you !