Time-resolved Fourier transform infrared emission spectra of HNC/HCN K. Kawaguchi A. Fujimoto...
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Transcript of Time-resolved Fourier transform infrared emission spectra of HNC/HCN K. Kawaguchi A. Fujimoto...
Time-resolved Fourier transform infrared emission spectra of HNC/HCN
K. Kawaguchi & A. FujimotoOkayama University
Introduction HNC : metastale isomer of HCN 0.62 eV higher energy isomerization reaction
In low-temperature interstellar clouds [HNC] 〜 [HCN] (T. Hirota, ApJ, 1998) Branching ratio in recombination reaction HCNH+ + e → HCN, HNC, CN
[HCN]/[HNC] 〜 3 (T, Amano et al. 2004) Time-resolved Infrared emission spectra
Data Sampling in a FT Spectrometer
He-Ne Laser
Samplingfor IR data
= 15803 cm-1
< 8000 cm-1
SpectrumFourier Transform
Interferogram
Path difference
- 200 - 100 0 100 200 300 400
Time (sec)
Timing diagram for TRFTSScan signal
He-Ne laser
Pulse event
Sampling in usual TRFTS
Sampling in our system
T Many scansare required
One scan
Block diagram of TRFTS system
ADC 432216 bit
≲ 2 MHz
New methodSX is replaced by FPGA(Field Programmable Gate Array)
Pulse discharge and time resolved spectra
Scan
He-Ne
DischargeTrigger
AD Trigger
100sec
(64)
64 interferograms
Fourier Transform
Max. 64 Spectra at preset time intervals
Bruker
Bruker
SX
SX
PC, C++
PC, C++
Performance of time-resolved FT
1. wavenumber resolution : 0.008 cm-1
2. time resolution : 0.5 sec (FPGA)3. pulse event frequency : < 40 kHz4. number of time-resolved spectra resolution : up to 0.04 cm-1 : 64 0.016 cm-1 : 32 0.008 cm-1 : 16
Emission
CH4( 15mT)C2H3CN( 10mT)He ( 1.35 T ) N2 ( 120 mT )
He( 6 T) H2( 60 mT)
anodeHe
watercathode
Expanded polystyrene
Pump
Liq.N2
Dry ice( in ethanol)
Window
discharge
Emission cell
Emission spectra of HCN, HNC ( at 77K) (32s)
HCN
HNC
P(9)
P(17)
P(3)R(8)R(2
)R(15)
P(9)
P(3)P(14)
R(9)
R(16)
R(3)
1(100-000)
(101-001)
(200-100)
1(100-000)
(101-001)
(200-100)
3050 3100 3150 3200 3250 3300 3350 34000
10 126 sec
wavenumber (cm- 1)
0
10 102 sec
0
10
0
10
78 sec
54 sec
0
10
0
10
30 sec
6 sec
HCN emission
200 KCH4 + N2
60 points3 sec step
0-180 sec covered
(300-200) (200-100) (100-000)
0 20 40 60 80 100 120 140 160 180 200
123456789
101112131415161718
HCN (300) - (200)
HCN (200)- (100)
HCN (100)- (000)em
ission
inte
nsity
time (sec)
Discharge 0-20 sec 200 K CH4 + N2
Vibrationalrelaxation
5 times shorterthan CO
Time variation of emission spectra (at 77 K)HCN
N2 HNC
2s
12s 22s
32s
42s
52s
Time variation of emission spectra (at 200 K)
2s
12s
22s
32s
42s
52s
HCN
HNC
( emission intensity of hot band : x 3 )
Time profile of emission intensities of HCN, HNC
liq. N2
Temp.
Dry iceTemp.
0 10 20 30 40 50 603000
3500
4000
4500
5000
5500
6000
dischargeon
HNC (200)- (100) (x 3)
HCN (200)- (100)em
ission
inte
nsity
time (sec)
Decay from (200) states of HNC and HCN
77 K
3316 3317 3318 3319 3320 3321
0
5000
10000
HCN Liq. N2 Temp.
30 spectra are shown by different colors
N2 electronic
3316 3317 3318 3319 3320 3321
0
5000
10000
3316 3317 3318 3319 3320 3321
0
2000
4000
HCN emission : Comparison in two conditions
77 KCH4 + N2
200 KC2H3CN+ H2
(100-000)(101-001)
(110-010)
3622 3623 3624 3625 3626- 1000
0
1000
2000
3000
4000
5000
6000
7000
3622 3623 3624 3625 3626
0
400
800
77 KCH4 + N2
200 KC2H3CN+ H2
HNC emission (100-000) P(9)(101-001)P(6)
N2
Decay from (101) is fastercompared with above
Temperature and/or chemical
Results (1)Tvib, Trot ( 2s after turning off the discharge) ● liq. N2 temp.
Tvib ・・・ HCN 3350 (± 250) K HNC 2200 K Trot ・・・ HCN 263 (± 2) K HNC 340 (± 40)
K ● dry ice temp. Tvib ・・・ HCN 2750 (± 250) K HNC 2400 K Trot ・・・ HCN 379 (± 6) K HNC 480 (± 7) K
Emission : increased after discharge-offIf the increment is due to reactions, abundance ratio ● liq. N2 temp. [HCN] : [HNC] = 40 : 4.3 ● dry ice temp. [HCN] : [HNC] = 10 : 1
Results (2)1. decay from HNC (200) is fast (10 sec) compared with that of HCN (200) HNC – HCN conversion?2. bending excited states : up to v2=2 (120)
production vibrational relaxation 3. decay from (101) of HNC is fast in (C2H3CN + H2) discharge at 200 K
vibrational relaxation
HNC-HCNconversion
HNC
HCN
AcknowledgmentsK. Manabe Ibaraki UniversityT. Amano (Ibaraki University)