How can synchrotron-based FTIR spectroscopy contribute to astrophysical and atmospheric data needs?

A.R.W. McKellar National Research Council of Canada, Ottawa

Herschel Space

Telescope

James Webb Space

Telescope

ALMA Atacama

Large Millimeter

Array

SOFIA StratosphericObservatory For Infrared Astronomy

ACE Atmospheric

Chemistry Experiment

ENVISAT

MetOp OCO (non)Orbiting Carbon

Observatory

Terahertz Remote SensingBillions of $ invested worldwide in THz and IR astronomical and atmospheric missions.

In many cases, the required laboratory data are unavailable, insufficient, or unreliable.

Can synchrotron FTIR help to address this problem?

Synchrotron-based IR spectroscopy

• For some IR applications, SR offers no advantage• But for high spatial resolution (condensed-phase

studies), or very high spectral resolution (gas-phase studies) the brightness of SR is ideal

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Here, SR gives us 5 to 25 times more signal through a 2 mm aperture than a conventional source. This promises up to 600 times faster data acquisition.

Synchrotron-based IR spectroscopy

• The synchrotron is simply providing a bright continuum source (like a very expensive globar)

• High spectral resolution IR is new for synchrotrons – pioneered at MAXLab and LURE

• New user facilities for high-res (gas-phase) IR spectroscopy are now starting up at CLS, SOLEIL, and the Australian and Swiss Synchrotrons

• Synchrotron advantage is presently limited by noise – mechanical vibrations of the beamline mirrors

High resolution synchrotron IR spectroscopy was pioneered by Bengt Nelander at MAXLab in Lund, Sweden These photos are from 2004

FIR Beamline AILES at Synchrotron SOLEIL near Paris

PascalRoy

Olivier Pirali

The Australian SynchrotronMonash University, near Melbourne

Swiss Light SourcePaul Scherrer Institute, Villigen

(between Zurich and Basel)

Singapore Synchrotron Light SourceISMI infrared beamline

Canadian Light SourceSeptember, 2008

January, 2009

CLS ParametersEnergy: 2.9 GeV

Current: 200 mA

Circumference: 171 m

12 straight sections, 5.2 m long

RF: 500 MHz, 2.4 MV, supercon

Injection: 250 MeV LINAC full energy booster ring

Main building: ~ 85 x 85 m

Bruker IFS 125 HR spectrometer: max optical path difference = 9.4 m instrumental resolution ~ 0.0006 cm-1 (18 MHz)

0.3 m gas cellabsorption paths up to 12 m

2 m gas cellabsorption paths up to 80 mcoolable to ~80 K

Synchrotron-based IR spectroscopy

• With continuing improvements, SR now has a significant advantage from 100 ~ 800 cm-1 at CLS

But we are aiming for better performance

• Reduce noise at source: better isolation of offending cooling pumps, heat exchangers, pipe runs, etc.

• Reduce noise at beamline: more isolation, better mounting of beamline mirrors

• Active optics to stabilize the input radiation on the spectrometer aperture

AcroleinCH2CHCHO(propenal)

• fundamental 8-atom species• planar near-prolate asymmetric rotor • interstellar molecule• combustion byproduct

(forest fires)• potent respiratory irritant (cigarette smoke, smog) E

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low lying vibrational states of acrolein

17 band of acrolein, CH2CHCHO

Ka = 7 – 6Q-branch

nominal resolution 0.0012 cm-1

Wavenumber / cm-1

611.3 611.4 611.5 611.6 611.7

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Synchrotron, 32 scans

Globar, 300 scans

Synchrotron, 414 scans

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simulation

2 m cell, 0.13 Torr

0.3 m cell, 0.8 Torr

0.0007 cm-1

Acrolein 18 central region

Wavenumber / cm-1

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Acrolein2 m cell, 0.13 Torr

Doppler width ~0.00026 cm-1

Pressure broadening ~0.00050 cm-1

Instrumental width ~0.00064 cm-1

0.0007 cm-1

Acrolein 18 central region

With 0.0007 cm-1 line width and reasonable signal-to-noise ratio, positions can be measured to <<0.0001 cm-1 (for unblended lines).

Half of the acrolein lines here are measured to 0.00003 cm-1 (1 MHz !!) or better.

Pyrrole (c-C4H4NH) 16 bandD.W. Tokaryk & J. Van Wijngaarden (2008)

Azetidine (C3H6NH), 16 bandJennifer van Wijngaarden,

University of Manitoba

400.0 450.0 500.0 550.0 600.0 650.0 700.0 750.0 400.0 450.0 500.0 550.0 600.0 650.0 700.0 750.0

512.0 513.0 514.0 515.0 516.0 517.0 518.0 519.0 520.0 521.0 522.0 523.0 512.0 513.0 514.0 515.0 516.0 517.0 518.0 519.0 520.0 521.0 522.0 523.0

516.6 516.8 517.0 517.2 517.4 517.6 517.8 518.0 518.2 518.4 518.6 518.8 519.0 519.2 516.6 516.8 517.0 517.2 517.4 517.6 517.8 518.0 518.2 518.4 518.6 518.8 519.0 519.2

qQ[(2,5)-(0,4)E]qQ[(3,-10)-(1,-9)E]

qR[(2,14)-(0,13)E]

Methanol (CH3OH) - new high torsional assignmentsL.-H. Xu, R.M. Lees, University of New Brunswick

(vt, K)

CDF3 4 / 3+6 band systemA. Predoi-Cross, LethbridgeP. Pracna, PragueA. Ceausu-Velcescu, PerpignanB. Billinghurst, CLS

CH3COD * 200 K * 48 m pathL.H. Coudert, LISA Université Paris 12

Wavenumber / cm-1

74.1 74.2 74.3 74.4 74.5

Abs

orb

ance

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0.5

1.0 acetaldehyde-d1

CH3CODT = 200 K

pressure = 0.3 Torrpath = 48 m

0.0007 cm-1

Wavenumber / cm-1

507.15 507.20 507.25 507.30 507.35

35Cl35ClCS

35Cl37ClCS

Sum

Experiment

Cl2CS (thiophosgene) 40 m path * 0.02 Torr

Wavenumber / cm-1

507.25 507.26 507.27 507.28 507.29 507.30

~ 0.00075 cm-1

Cl2CS 2 band

~1800 transitions fitted with rms deviation of 0.000065 cm-1 (2 MHz)

How can synchrotron-based FTIR spectroscopy contribute to astrophysical and atmospheric data needs?

Compared to conventional IR sources, synchrotrons promise a combination of– Higher spectral resolution– Higher signal-to-noise ratio– Shorter observation time– Better matching to absorbing molecules (e.g. supersonic jet)

But as observation time becomes shorter we become limited by– Time for sample preparation and change

(e.g. in a large cooled gas cell)– Time for data analysis!!

Coherent Synchrotron Radiation

Wavenumber / cm-1

10 12 14 16 18 20 22 24 26

12 14 16 18 20 22 24 26 J"

N2O pure rotational transitions recorded with coherent synchrotron radiation

Coherent Synchrotron Radiationtends to be noisy because of its nonlinear nature and the presence of beam instabilities

Science Goals Complexes & Clusters

Important intermolecular vibrations are located in the far IR. Spectroscopy directly measures intermolecular forces, important for fields like molecular collisions, condensation, solvation, and energy transfer; also provides stringent & unambiguous tests for quantum chemistry calculations. Sampling techniques: cooled long-path cell; future supersonic jet.

THz Laboratory Astrophysics: Ions & Radicals Far IR is now being explored by astronomers with new aircraft-, space-, and ground-based observatories. It’s the natural wavelength region for observing ‘cool’ matter in the universe (e.g. stellar and planetary formation).

modular 1.5 m gas discharge cellfor unstable astrophysical radicals