FOURIER TRANSFORM FAR-INFRARED SPECTROSCOPY OF HN2

+ ON THE AILES BEAMLINE OF SYNCHROTRON SOLEIL

O. Pirali, S. Gruet, M. VervloetAILES beamline, synchrotron SOLEILInstitut des Sciences Moléculaires d’Orsay

Caracteristics of SOLEIL facility

Storage mode :

« Top-up » 430 mA« multibunches »: 416 bunches« temporel » : 8 bunches

Bunch of electrons accelerated in the LINAC to 100 MeV

Accelerated in the Booster to 2.75 GeV

Injected in the storage ring (113 m diameter)

Dipoles, undulators, wiggler to make the electrons « oscillating »Loss of energy throught photon emission

Length of a bunch : 10 psPeriod between bunches : 10 ns

www.synchrotron-soleil.fr

Call for beamtime every 6 monthshttp://sunset.synchrotron-soleil.fr/sun

FIR absorption spectroscopy of transient species

14NH2, 15NH2, C3,CH, NH,OH, SH, SO (TD12)

DC DISCHARGE

• ~ 1KV / 100mA • 24 m absorption• White type cell• Continuum synchrotron• RESOLUTION=30MHz• 20-700 cm-1

PhD Marie-Aline Martin (2012)

HN2+, HCO+, H3

+

PhD Sebastien Gruet

Schematic view of the hollow cathode discharge cell

10 cm

Teflon ringsLiquid N2

(output)

Evacuation

Anode

70 cm Gas Injection

110 cm

Hollow Cathode

Windows

Beam

15 cm

Liquid N2 (input)

Pyrex Cell

Technical details

Gold mirrors

Copper electrodes

Absorption path length: 16-24 m

Max pumping speed : 250 m3.h-1

Min. cathode temperature : 77 K

See e.g. S. Foster et al., J. Chem. Phys., 81,578 (1984)

Spectroscopy of cationic molecules

Experimental conditions :

Observations(1800 – 3800 cm-1)

Molecules H3+, HN2

+ & HCO+

Resolution H3+ (0.015 cm-1), HN2

+

& HCO+ (0.007 cm-1)

Source Internal NIR source

Detector InSb

Beamsplitter KBr

Windows CaF2

Iris H3+ (2.5 mm), HN2

+ & HCO+ (1.7 mm)

++ +

H3+ : HN2

+ : HCO+ :

Synchrotron radiationMichelson interferometer

New cell

Gases

Power supply

Liquid nitrogen tank

Pumping group

Detector

Wavenumber (cm-1)

Abso

rban

ceH3

+ Observation in the mid-Infrared

H3+ experimental details

Acquisition time Detector Band observed ResolutionNumber of transitions

Cathode temperature

45 min InSb 2 0.015 cm-1 28 77 K

2725.8 2725.9 2726.0 2726.1 2726.2 2726.3

0.00

0.01

0.02

0.03

0.04

0.05

0.06

Ab

sorp

tion

Wavenumber (cm-1)

77 K 144 K 185 K 214 K 271 K

Temperature dependance of the H3

+ abundanceSee McKellar and Watson, J. Mol. Spec, 191, 215 (1998)

Ro-vibrational spectra of HN2+ and HCO+ in mid-Infrared

3170 3180 3190 3200 3210 3220 3230 3240 3250 3260 3270 3280 3290

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

P(1

6)

P(1

5)

P(1

4) P

(13) P(1

2)

P(1

1)

P(1

0)

P(9

) P(8

)

P(7

)

P(6

)

P(5

)

P(4

)

P(3

)

P(2

)

P(1

)

Wavenumber (cm-1)

Ab

so

rba

nce

R(0

)

R(1

)

R(2

) R(3

) R(4

)

R(5

)

R(6

)

R(7

)

R(8

)R

(9)

R(1

0)

R(1

1)

R(1

2)

R(1

3)

R(1

4)

R(1

5)

HN2+

Trot (HN2+ & HCO+) ≈180K

Amano, J. Chem. Phys. 79, 3595 (1983).1st FT detection of the ν1 band of HCO+ ?

HCO+

Experimental details (HN2+ and HCO+)

Band Acquisition time Jmax Number of transitions Resolution

1 25 min 15 (HN2+), 14 (HCO+) 32 (HN2

+), 29 (HCO+) 0.007 cm-1

H3+ + X HX+ + H2 X = N2, CO

Protonation of neutral species :

Nakanaga et al., Chem.Phys. Lett., 169, 269 (1990)

9

Pure rotational transition of HN2+ in the far-Infrared

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

Wavenumber (cm-1)

Ab

sorb

an

ce

24.80 24.85 24.90 24.95

J = 11 10J = 9 8

J = 12 11J = 10 9

J = 8 7

27.90 27.95 28.00 28.05

31.00 31.05 31.10 31.15

34.10 34.15 34.20 34.25

37.20 37.25 37.30 37.35

R(J) J’ – J’’ Our work (MHz) Published frequencies (MHz) Difference (MHz)7 8 - 7 745214(15) 745209.868(30)a 4.18 9 - 8 838300(15) 838307.1(10)b -7.19 10 - 9 931374(15) 931386.2(10)b -12.2

10 11 - 10 1024435(15) 1024443.2(10)b -8.211 12 - 11 1117481(15) 1117477.1(12)b 3.9

Poor S/N ratioFirst FT pure rotation5 transitions recordedGood agreement with the literature

Acquisition15-40 cm-1

HN2+

0.0025 cm-1

Synchrotron radiation

1.6 K cooled Bolometer

50 µm Mylar

Polypropylene

10 mm

a Amano et al., J. Mol. Spec, 234, 170 (2005)b Verhoeve et al., Rev. Sci. Instrum., 61, 1612 (1990)

Attempt using Coherent Synchrotron Radiation…

“coherent” : ITHz linear with Iring2

“ incoherent” : ITHz linear with Iring

• B. Billinghurst et al., Optics letters, 35, 3090 (2012)• PhD J. Barros (2012) • Barros et al., Rev.Sci. Instrum., 84, 033102 (2013)• See talk WH15

11

Conclusion and perspectives

• Ion density : 1011 molecules.cm-3

• Necessity to obtain higher density of ions

• ≠ cathode materials, new discharge geometry

• Improve the cooling system

Aknowledgements

AILES Staff :S. Gruet, P. Roy (BML manager), L. Manceron, J. B. Brubach, M. Chapuis, F. Alabarse, S. Dalla Bernardina