Time-resolved Fourier transform infrared emission spectra of HNC/HCN K. Kawaguchi & A. Fujimoto Okayama 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 Sampling for IR data = cm -1 < 8000 cm -1 Spectrum Fourier Transform Interferogram Path difference

Timing diagram for TRFTS Scan signal He-Ne laser Pulse event Sampling in usual TRFTS Sampling in our system TT Many scans are required One scan

Block diagram of TRFTS system ADC bit ≲ 2 MHz New method SX is replaced by FPGA (Field Programmable Gate Array)

Pulse discharge and time resolved spectra Scan He-Ne Discharge Trigger AD Trigger 100  sec (64) 64 interferograms Fourier Transform Max. 64 Spectra at preset time intervals Bruker SX PC, C++

Performance of time-resolved FT 1. wavenumber resolution : cm time resolution : 0.5  sec (FPGA) 3. pulse event frequency : < 40 kHz 4. number of time-resolved spectra resolution : up to 0.04 cm -1 : cm -1 : cm -1 : 16

Emission CH 4 （ 15mT ） C 2 H 3 CN （ 10mT ） He （ 1.35 T ） N 2 （ 120 mT ） He （ 6 T ） H 2 （ 60 mT ） anode He water cathode Expanded polystyrene Pump Liq.N 2 Dry ice （ in ethanol ） Window discharge Emission cell

Emission spectra of HCN, HNC ( at 77K) (32  s) 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 ( ) ( ) ( ) 1 ( ) ( ) ( )

HCN emission 200 K CH 4 + N 2 60 points 3  sec step  sec covered ( ) ( ) ( )

Discharge 0-20  sec 200 K CH 4 + N 2 Vibrational relaxation 5 times shorter than CO

Time variation of emission spectra (at 77 K) HCN N2N2 HNC 2s2s12  s22  s 32  s 42  s52  s

Time variation of emission spectra (at 200 K) 2s2s12  s 22  s 32  s 42  s 52  s HCN HNC

（ emission intensity of hot band : x 3 ） Time profile of emission intensities of HCN, HNC liq. N 2 Temp. Dry ice Temp.

Decay from (200) states of HNC and HCN 77 K

HCN Liq. N 2 Temp. 30 spectra are shown by different colors    N 2 electronic

HCN emission : Comparison in two conditions 77 K CH 4 + N K C 2 H 3 CN+ H 2 ( )( ) ( )

77 K CH 4 + N K C 2 H 3 CN+ H 2 HNC emission ( ) P(9) ( ) P(6) N2N2 Decay from (101) is faster compared with above Temperature and/or chemical

Results (1) T vib, T rot ( 2  s after turning off the discharge) ● liq. N 2 temp. T vib ・・・ HCN 3350 (± 250) K HNC 2200 K T rot ・・・ HCN 263 (± 2) K HNC 340 (± 40) K ● dry ice temp. T vib ・・・ HCN 2750 (± 250) K HNC 2400 K T rot ・・・ HCN 379 (± 6) K HNC 480 (± 7) K Emission : increased after discharge-off If the increment is due to reactions, abundance ratio ● liq. N 2 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 v 2 =2 (120) production vibrational relaxation 3. decay from (101) of HNC is fast in (C 2 H 3 CN + H 2 ) discharge at 200 K vibrational relaxation

HNC-HCN conversion HNC HCN

Acknowledgments K. Manabe Ibaraki University T. Amano (Ibaraki University)