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Terahertz spectroscopy of molecules, radiacls and ions using
Evenson-type tunable FIR spectrometer
Fusakazu Matsushima
Department of Physics,
University of Toyama, Japan
67th Columbus meeting, June 20, 2012
Scope of this talk“Evenson-type” = difference frequency of CO2 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+, H2D+) Molecular anion (OH-)
Extended negative glow discharge cell Temperature ( N2H+) Recent work (H2F+)
Ken. M. Evenson
NIST (Boulder, Colorado)Time & Frequency Division
late Ken. M. Evenson NIST (Boulder, Colorado)Time & Frequency Division
in 1993at Toyama
His wife called him “a man of curiosity”
“The final measurement of speed of light”
Talk in Toyama (1993)
MIM diode as detector / mixer
Chain for the measurement of CO2 laser frequency
Standard:Cs atomic clock
MIMdiode
whisker
CO2 laser lines
10P
10R
9P
9R
angle of grating
outp
ut p
ower
1. Frequency range
Distribution of CO2 laser lines
TuFIR (CO2 laser difference frequency)How to obtain the tunability
using wave guide CO2 laser using MW source
tunability ~ 100MHzneed many combinations
tunability ~ 20GHz
power: 2nd > 3rd
Evenson-type TuFIR in the world of 1990s
NIST (Corolado): 2nd, 3rd Minnesota (K.R. Leopold): (2nd?), 3rd LENS(M. Inguscio, Firenze, Italy): 3rd
Toyama: 3rd (2nd prepared)
NIST 2nd order system
TuFIR spectrometer
FIR=|I - II|±MW
MIM diode
micro wave
whisker
roof top mirror
base
FIR
CO2 laser
Properties
1. Frequency Range
2. Precision
3. Sensitivity ( Power of the radiation source)
Distribution of CO2 laser lines
≈ 5.5THz
upper or lower sidebanddifference freq. of two CO2 lasers
Fourier transform spectrometer
TuFIR
CO2 fluorescence cell
Laser frequency (cavity length)
4.3mfluorescence
1st derivative
Stabilization of the CO2 laser frequency
Accuracy of laser frequency table <2kHz
Accuracy of laser stabilization one CO2 laser 25kHz → difference freq. 36 kHz
2. Precision
NH3 s(J=7,K= 3 ) ← a(J=6,K= 3 )
4126502.441 4126477.036(37) 4126452.441Frequency(MHz)
9P(20)-10R(24) = 4138411.441 (MHz)MW =11909 ~ 11959 ( MH z)
Fitting with Voigt profile ⇒ center frequency
←Bolometer
Synthesized source power ( 3rd order TuFIR spectometer)
characteristics of the componentsin the detector
frequency characteristics of MIM diode
3. Sensitivity (Power of the source)
property of TuFIR spectrometer
1. frequency range about 30 GHz ~ 5.5 THz (or 6THz, 10THz)
2. measurement accuracy of spectral lineseveral tens kHz for strong (neutral) moleculesseveral hundres kHz for weak (ionic) molecules
3. power of the synthesized FIR several tens of nW ~ several hundreds of nW
Trials for extending the properties
1. Frequency range ⇒ higher order nonlinearity of MIM ⇒ use of NH3 laser2. Resolution ⇒ sample in a molecular beam
| νI ー νII | νMW = 2.4THz
9P(14)-10R(14) 2.4THz
| νI ー νII | 2 νMW = 2.4THz 10R(34)-10P(20) 1.2THz
1. Multiple of IR frequency
3 wave mix
5 wave mix
H218O
321 ← 312
up to 9.1THz
CO2 laser + NH3 laser
H. Odashima, L.R. Zink, & K.M. Evenson, Opt. Lett. vol.24, 406 (1999)
CH3OH(n=1,K=7,J=19)←(0,6,19)A-type transition
Maximum record of TuFIR
Effusive molecular beam
Multi channel array (diam 10μm, length 2mm)Optical Path length: about 30 cmStagnation pressure: 0.15 Torr effective sample pressure ≤ 1mTorr
2. Molecular beam
bulk gas2x10-4 Torr
beam
width= 220kHz (peak to peak)
H218O
432 ← 423
Molecules and ions measured with TuFIR spectrometer in Toyama
(1) neutral molecules , radicals
LiH, KH, 18 OH, NH, NH3
H2O ( H216O, H2
17O, H218O, D2O, and H2
16O (v2=1 excited state))
(2) molecules with internal rotation
CH3OH
(3) cation protonated rare gas atoms (HeH+ , NeH+ , ArH+ , KrH+ , XeH+ , including their isotopic species)
H2D+ , N2H+ , H2F+
(4) anion OH- , OD-
Part 2.
Discharge cell
1. Glow discharge cell dc discharge ac discharge: velocity modulation technique
Molecular cation (HeH+, H2D+) Molecular anion (OH-)
2. Extended negative glow discharge cell
dc discharge Temperature ( N2H+) Recent work (H2F+) collaboration: T. Amano (U. Waterloo) K.Kawaguchi (Okayama U.) R,Fujimori (Okayama U.)
(collaboration with Prof. Amano (Waterloo, Canada))
Fig.1 TuFIR 分光計
Velocity modulation:
detects ions only
Configuration for detecting ionic species
HeH+ J=10
The lowest frequency rotational line
2010.1839 (2) GHz
HeH+
Dunham coefficient Ykl
EvJ = ΣYkl(v+1/2 )k[J(J+1)]l
( a set of coefficientsYkl for each isotope)
To calculate all the isotopes with a set of coefficients Ukl
Ykl = μ-(k/2+l)Ukl
Reduced mass μis not enough to fit all the isotopes.
Ykl = μ-(k/2+l)Ukl [1+meΔHekl/MHe + meΔH
kl/MH] Correction terms usingΔvalues are necessary.
Breakdown of Born-Oppenheimer approximation.
HeH+ Rotational Transition
transition frequency obs-calc
4HeH+ J=10 2010183.873 (202) 0.108J=21 4008733.084 (194) -0.148
4HeD+ J=21 2434626.571 (143) 0.077 J=32 3641427.274 (384) -0.210
J=43 4835691.417 (166) 0.039
3HeH+ J=10 2139522.472 (300) -0.213J=21 4265839.060 (300) 0.330
3HeD+ J=21 2696099.975 (255) -0.021 J=32 4031223.001 (511) -0.650
HeH+
HeH+ : 3HeH+, 4HeH+, 3HeD+, 4HeD+
NeH+ : 20NeH+, 20NeH+, 22NeD+, 22NeD+ ArD+ :
KrH+ : 82KrD+, 84KrD+, 86KrD+, 82KrH+
XeH+ : isotopes of 124Xe, 126Xe, 128Xe, 129Xe, 130Xe, 131Xe, 132Xe, 134Xe, 136Xe,
and H, D
protonated rare gas atoms
typical trace of H2D+
211 110
H2D+
H2D+
J =3← 2
3363550.5413363550.541 frequency frequency (( MHzMHz ) ) 3363658.5413363658.541intensity(arb. units)
intensity(arb. units)
OH-
transition frequency (MHz) J=43 4478174.516 (387) J=32 3363607.066 (238) J=21 2244776.819 (240) J=10 1123100.985 (324)
OD-
Frequency(MHz)
Frequency(MHz)Frequency(MHz) Frequency(MHz)
Frequency(MHz)
J=2←1 J=3←2
J=5←4 J=6←5 J=8←7
Inte
nsi
ty
(arb
.un
its)
Inte
nsi
ty
(arb
.un
its)
Inte
nsi
ty
(arb
.un
its)
Inte
nsi
ty
(arb
.un
its)
Inte
nsi
ty
(arb
.un
its)
D2O/O2=54.5/5Pa,AC1.2kHz,1.1A,4.8kV,Scan6 回 ,エタノール冷却 2 ,℃ 湿度 60%,FIR200mV( 100nW)≒
ND3/O2=35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回 ,水冷 , 湿度 29%,FIR140mV( 70nW)≒
ND3/O2=35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回 ,水冷 , 湿度 26%,FIR160mV( 80nW)≒
D2O/O2=23.5/5Pa,AC1.2kHz,1.2A,4.5kV,Scan3 回 ,水冷(溜め置き) , 湿度 60%,FIR150mV( 75nW)≒
ND3/O2=35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回 ,水冷 , 湿度 24%,FIR40mV( 20nW)≒
Fit 1196791.042(0.486)MHz
OH-, OD-
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 !!
N2H+ J=14 ← 13 E" = 283 cm-1
N2:H2:Ar=0.9 ; 0.9 : 2Pa7mA, 1.7kV
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
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
T = 129K
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
N2H+ J=14 ← 13 E" = 283 cm-1
Lig. Nitrogen cooling
Water cooling
nothing !
N2H+ J=5←4 temperature dependence, sub-mm spectrometer (by Amano)
-200C (liq. N2 temp)-100 -85 -65 -30 -15 -5 +20 (room temp.)
H2F+
⇒ H2F+ in space?
Fluorine contained species detected in space. (interstellar space, circumstellar envelopes)
AlF, HF, CF+
H2Cl+ 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
Previous laboratory measurements for H2F+
IR Laser spectroscopy with velocity modulation technique
Schäfer and Saykally, J. Chem. Phys. 81, 4189 (1984) ~ 3 µm region, ν1 and ν3 bands FTIR Fujimori, Hirata, Kawaguchi, and Morino, International Symposium
on Molecular Spectroscopy (Columbus, OH), 2010. ν2 band in addition to ν1 and ν3 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
Astrophys. J. Lett., 729 L2 (2011)
Length: ~ 1.3mVoltage: 2 ~ 3kVCurrent: ~10mAT: 0 ~ -70 C
HF : H2 : Ar = 0.2 : 1 : 2Pa
Extended negative glow discharge cell with ethanol cooling
HF heat cell: preparedby Fujimori & Kawaguchi
H2F+ 303 ← 212 T= -70C
H2F+ 111←000
1305306.600 (56) MHz
H2F+
111-000 1305306.503 (073) MHz303-212 1370911.418 (048)413-404 1425857.036 (059)523-514 1737165.499 (066)422-413 1748037.582 (085)321-312 1823629.057 (070)212-101 1850081.989 (050)
H2F+: isoelectronic to H2O, mass close to H218O
red arrow: TuFIR
Lowest frequency rotational lines
para111-000 1305306.503 (73) MHz(TuFIR measurement, Toyama)
ortho110-101 760928.937 (10) MHz(sub-mm measurement, Waterloo)
liq. N2 cell without glass-blowing
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 speciesT. Amano (Univ. Waterloo, Canada) --- ext. neg. glow discharge cell and works using itK. Kawaguchi (Okayama Univ.)late J.M. Brown (Oxford Univ.)
and of course
late K.M. Evenson (NIST Boulder Colorado)
Thank you !