THz SPECTRUM OF METHYL BROMIDE (CH3Br)Marlon Ramos and Brian J. Drouin

6/23/2011 1THz Spectrum of Methyl Bromide (CH3Br)

INTRODUCTION TO CH3Br

Natural:

• Oceans: • Algae, Kelp

• Continental :• Vegetation, biomass burning

Sources of CH3Br

Commercial:

• leaded gas

• pesticide

• fire retardant

6/23/2011 2THz Spectrum of Methyl Bromide (CH3Br)

INTRODUCTION TO CH3Br

Commercially man-made sources have led to an increase of CH3Br levels in our atmosphere:

• CH3Br has an ozone depletion potential of 0.2% and falls under regulations of the Clean Air Act b

Constant exposure to CH3Br is highly toxic a:

• Long term Inhalation of 1,600 ppm in a time interval of [10,20] hours, or 7,900 ppm for 1.5 hours is lethal to humans or can also lead to neurological damage

• Short term exposure might cause lung damage to humans

Reasons to monitor CH3Br

THz Spectrum of Methyl Bromide (CH3Br) 6/23/2011 3

INTRODUCTION TO CH3Br

Because It is an ubiquitous component of our earth’s atmosphere and of because of increasingly concerning levels of CH3Br In our oceans and atmosphere:

• The California Birth Defects Prevention Act of 1984 (SB 950) requires that all pesticides (such as CH3Br) be supported by health testing data.

• In 1991, the for ‘lack of testing data,’ the EPA scheduled a phase-out of CH3Br, which started in the year 2000.

Response to CH3Br

6/23/2011 4THz Spectrum of Methyl Bromide (CH3Br)

MOLECULAR SPECTROSCOPY IS USEFUL FOR MONITORING

OZONEOzone Depletion Process

Cycle happens in the stratosphere at tropical and middle latitudes where ultraviolet sunlight is most intense.

Cycle begins with BrO or Br

BrO with O = Br

Br with reacts by destroying ozone and reforming BrO, loops all over again.

Br or BrO is reformed each time an ozone molecule is destroyed, Br is considered a catalyst for ozone destruction. Atomic oxygen (O) forms when ultraviolet sunlight reacts with ozone and oxygen molecules

6/23/2011 5THz Spectrum of Methyl Bromide (CH3Br)

INTRODUCTION TO CH3Br

Even though CH3Br might seem very useful and promising, its use has environmental impacts and health concerns.

How do we accurately measure levels of CH3Br in our environment?

Microwave Limb Sounding?BrO - N.J. Livesey, et. al,

Geophys. Res. Lett. 33 (2006) L20817.CH3Cl - N.J. Livesey, et. al,

JPL publication D-33509; http://mls.jpl.nasa.gov/data/v3-3_data_quality_document.pdf

Accurately measure and detect CH3Br will allow us a better understanding of its effect in our environment.

Thoughts on CH3Br

6/23/2011 6THz Spectrum of Methyl Bromide (CH3Br)

PREVIOUS WORK ON CH3Br’s SPECTRUM

1) W. Gordy, J. W. Simmons and A. G. Smith, Phys. Rev. 74 (1948) 243 – 249.

2) A. H. Sharbaugh, J. Mattern, Phys. Rev. 75, (1949) 1102 .3) J. W. Simmons, W. O. Swan, Phys. Rev. 80, (1950) 289 .4) J. W. Simmons, W. E. Anderson, Phys. Rev. 80, (1950) 338 .5) J. Kraitchman, B. P. Dailey, J. Chem. Phys. 22, (1954) 1477 .6) W. J. Orville Thomas et al., J. Chem. Phys. 22, (1954) 1718 .7) Y. Morino and C. Hirose, J. Mol. Spec. 24 (1967) 204 – 224.8) T.E. Sullivan, L. Frenkel, J. Mol. Spec. 39 (1971) 185 – 201. 9) J. Demaison et al., J. Chem. Phys. 67, (1977) 254 .10)B. Duterage, et. al, Compt. Rend. Acad. Sci. Paris B, 284 (1977)

213 - 215.11) M. V. Moskienko, S.F. Dyubko, Opt. Spectrosc., 43, (1977) 503.12)K.-F. D¨ossel, D. H. Sutter, Z. Naturforsch 34a, (1979) 469.13) J. R. Williams, S. G. Kukolich, J. Mol. Spectrosc. 74, (1979) 242. 14)W.A. Wensink et al., J. Phys. B 13, (1980) 4009 .15) S. G. Kukolich, C. D.Cogley, J. Chem. Phys. 77 (1982) 1685;

erratum 77, (1982) 581.16) R. Bocquet et al., Europhys. Lett. 2 (1986) 275 . 17)R. Bocquet et al., J. Mol. Spectrosc. 164, (1994) 456. Axial Constants (from IR GSCDs)18)F. Lattanzi, C. di Lauro, G. Guelachvili, Mol. Phys. 45 (1982) 295. 19)J. Sakai, M. Katayama, J. Mol. Struct. 190 (1988) 113. 20)F. Kwabia Tchana, et. Al, J. Mol. Spectrosc. 228 (2004) 441 - 452.

6/23/2011 7THz Spectrum of Methyl Bromide (CH3Br)

Focus on Rotational data and infrared ground state combination differences SPFIT/ SPCAT (suite) is used to fit the data which in turn generates predictions for the JPL catalog.Most data of high quality especially in the millimeter wavelengths:

1) T.E. Sullivan, L. Frenkel, J. Mol. Spec. 39 (1971) 185 – 201. 2) J. Demaison et al., J. Chem. Phys. 67, (1977) 254 .3) B. Duterage, et. al, Compt. Rend. Acad. Sci. Paris B, 284 (1977) 213

- 215.

Submillimeter work was ok up to 800 GHz, but marginal above

1) R. Bocquet et al., Europhys. Lett. 2 (1986) 275 . 2) R. Bocquet et al., J. Mol. Spectrosc. 164, (1994) 456.

Very little work done on 13CH3Br

We happened to have a sample of 90% enriched 13CH3Br

CRITICAL EVALUATION FOR CATALOG

6/23/2011 8THz Spectrum of Methyl Bromide (CH3Br)

Experiments were performed at room temperature utilizing an isotopically (90%) enriched sample of 13CH3Br . Spectra were recorded from 750 - 1200 GHz, assignments where made that covered CH3

79Br, CH381Br, 13CH3

79Br and 13CH381Br isotopologues at J < 66 and K < 17

for the ground vibrational states.

12CH3Br transitions where observed at 10% the signal level of corresponding to 13C transitions. During detection, the pressure chosen for 13CH3Br produced saturation of lines at J≤66 and K≤9.

EXPERIMENTAL PROCESS

6/23/2011 9THz Spectrum of Methyl Bromide (CH3Br)

OBSERVED CH3Br SPECTRUM4 sources scanned from 750-1200 GHz

at 200 kHz resolution - 1.5 million data points!

H2O (atmospheric

spectrum)Overlap

of sources

Gap between sources

All data

6/23/2011 10THz Spectrum of Methyl Bromide (CH3Br)

OBSERVED CH3Br SPECTRUM

At 0.8 THz

J = 41

Spectra of 12CH379Br

6/23/2011 11THz Spectrum of Methyl Bromide (CH3Br)

OBSERVED CH3Br SPECTRUM

At 1.2 THz

J = 61

Spectra of 12CH379Br

6/23/2011 12THz Spectrum of Methyl Bromide (CH3Br)

HAMILTONIAN FOR CH3Br SPECTRUM

Model used to fit the spectrum , which can determine A, B, D, H

4

2333

33

2

)1(2

)1(4])2[(

114

)1(2)1(2

KJH

KJHJJ

JHJD

KJDJB

JKK

JJK

JJ

JK

Transition Frequency (with J’ = J” + 1, K’ = K”) between two adjacent energy levels

64

222

334

222

2

1

1

1

11

1)(/

KHJJKH

JJKH

JJHKD

JJKDJJD

JBJKBAhE

KJKK

JJK

JK

JKJ

Equation for any energy level (of Rotation)

Energy and Transition states:

Lowest = Ground State, Highest = Upper State, Middle = Transitional

6/23/2011 13THz Spectrum of Methyl Bromide (CH3Br)

MEASURED FREQ.’S OF CH3Br

Frequency precision fits to 8 significant figures, our model fits to all eight

6/23/2011 14THz Spectrum of Methyl Bromide (CH3Br)

FITTING RESULTS FROM FIT OF

CH3Br PARAMETERS

fixed axial and hfs for 13C

6/23/2011 15THz Spectrum of Methyl Bromide (CH3Br)

FITTING RESULTS FROM FIT OF

CH3Br STATISTICS

* All of the residuals were biased positive

6/23/2011 16THz Spectrum of Methyl Bromide (CH3Br)

FITTING RESULTS FROM FIT OF

CH3Br n3 PARAMETERS

6/23/2011 17THz Spectrum of Methyl Bromide (CH3Br)

CH3Br is an important species known to be active in our

atmosphere.

It is important to improve the understanding of less complex

molecules in order to have a better understand on how to approach

more complex molecules.

This study improves the spectroscopic database for CH3Br at the

1.2 THz range

We have submitted a manuscript for publication to the Journal of

Molecular Spectroscopy , describing this work and the results.

Microwave limb sounding (MLS) is currently detecting methyl

chloride (CH3Cl )and Bromine monoxide (BrO); utilizing their THz

spectra, we hope this characterization of the THz spectrum of CH3Br

will lead to a method to monitor it globally .

CONCLUSION

6/23/2011 18THz Spectrum of Methyl Bromide (CH3Br)

Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena, Californiawww.nasa.gov

NASA Undergraduate Student Research Program (USRP)

ACKNOWLEDGEMENTS

Molecular Spectroscopy Group : Timothy Crawford, Shanshan Yu, Harshal Gupta and Keeyoon Sung

Petra.A.Kneissl-Milanian (USRP Advisor)

6/23/2011 19THz Spectrum of Methyl Bromide (CH3Br)