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PB88-110051

NO2 Heterodyne Frequency Measurements with aTunable Diode Laser, a CO LaserTransfer Oscillator, and CO2 Laser Standards

(U.S.) National Bureau of Standards (NML)Boulder, CO

Prepared for

National Aeronautics and Space AdministrationWashington, DC

Apr 87

as. 94011W 40 o^Qwo.r reta kf..fs 3 k

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1 + NP'3 TECHNICAL NOTE 1308

REPRODUCEDBYU.S. DEPARTMENT OF COMMERCE

NATIONAL IECHN.CALINFORMAT ION SEI.V JESPRINGFIELD, VP 2" 16t

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4. TITLE AND SUBT!TLE

NO2 Heterodyne Frequency Measurements With a Tunable Dinde Laser,A CO Laser Transfer Oscillator, and CO 2 Lasser Standards

S. AUTHCR(S)L. R. 'Link, M. Vanek, and J. S. Wells

6. PERFORMING ORGANIZATION (If joint or other than N@S, see instructions) 7. Contract/Grar.t No.

NATIONAL BUREAU OF STANDARDSDEPARTMENT OF COMMERCE g. Type of Report & Period CoveredWASHINGTON, D.C. 20234

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Supported in part by Upper Atmospheric Research Officer NASANBS Category No►

NBS. N-1010. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summery, is attached.11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)Heterodyne frequency measurements have been made on selected groups of

nitrogen dioxide rovibronic transitions between 1580.8 and 1650.7 cm 1.

The groups are separated by 7 to 10 cm -1 , and the intent is to ,

I provide a limited (and interim) calibration table for the region. In

Iaddition to a table of measured frequencies in this region, we have

included figures of spectra in the vicinity of the measured lines to

provide a map for identifying the transitions measured.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and s,^oarate key words by semicolons)calibration frequencies at 6.2 pm; heterodyne frequency measurements;

nitrogen dioxide spectra

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USCOMM-DC e4

NO2 Heterodyne FrequencyMeasurements With a Tunable DiodeLaser, a CO Laser Transfer Oscillator,and CO2 Laser Standards

L.R. ZinkM. VanekJ.S. Wells

Time and Frequency DivisionCenter for Basic StandardsNational Measurement LaboratoryNational Bureau of StandardsBoulder, Colorado 80303.3328

Supported in part byUpper Atmospheric Research OfficeNASA

♦ •`Mi

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: M~w fof o^

•`A[AU C^ y

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

1

Issued April 1987

I G

National Bureau of Standards Technical Note 1308Natl. Bur. Stand. (U.S.), Tech Note 1308, 28 pages (Apr. 1987)

CODEN:NBTNAE

U.S. GOVERNMENT PRINTING OFFICEWASHINGTON: 1987

1l

CONTENTS

ABSTRACT .................... ..............................1

INTRODUCTION ................ ..............................1

EXPERIMENTAL TECHNIQUES .... . ..............................4CONCLUSION .......................................... ...6ACKNOWLEDGMENT............ ................................6

REFERENCES .................. ..............................7

APPENDIX .................... .............................10

iii

NO2 HETERODYNE FREQUENCY MEASUREMENTS WITH A TUNABLE DIODE LASER,A CO LASER TRANSFER OSCILLATOR, AND CO` LASER STANDARDS

L. R Zink, M. Vanek, and J. S. WellsTime and Frequency DivisionNational Bureau of Standards

Boalder, Colorado 80303

y measurements have been made on selected groupsrovibronic transitions between 1580.8 and 1650.7

cm . The groups are separated by 7 to 10 cm 1, and the intent isto provide a limited (and interim) calibration table for the region.In addition to a table of measured frequencies in this region, wehave included figures of spectra in the vicinity of the measuredlines to provide a map for identifying the transitions measured.

Key words: calibration frequencies at 6.2 µm, heterodyne frequencymeasurements, nitrogen dioxide spectra.

INTRODUCTION

A program was established several years ago to provide reference frequen-

cies for the use of spectroscopists for the calibration of spectra. The

objectives at the initiation of the program (with particular emphasis on the

use of tunable diode lasers) were to select molecules meeting certain criter-

ion such as

1. Absorption type standards

2. A marker every 0.5 cm-1 (to match TDL mode tunability)

3. A convenient molecule (one easily handled)

4. A simple Hamiltonian

5. Line positions should be good to ± 3 MHz.

The last criterion requires heterodyne frequency measurements and that

has been a major task along with the selection and fitting of the best

available measurements from the literature. Some of the better candidates

were carbonyl sulfide (OCS) and nitrous oxide (NZ O). A large body of work has

been completed on OCS [1-5]. OCS has a fairly high abundance of isotopic

species which help provide a definite signature (spectroscopic pattern) in the

vicinity of a particular calibration feature. A 6600 entry OCS atlas (6),

Heterodyne frequencof nitrogen dioxide

-1

1

which gives the transition wavenumber, the transition frequency, the isotopic

species, the transition band, the J-value for the transition, the lower state

energy level and the intensity in a normal mixture for each line is available.

The coverage afforded by OCS shown in figure 1 below.

INFRARED FREQUENCY CALIBRATION STANDARDS

Key to accuracy

•.:. ;,,^"::•• adequa ► e accuracy ±10 MHz or better

11111 In t 10 to ±60 MHz

W2±60 MHz or worse

NO

DBrCOz

CzHz

OCS

N20SUM

nllln 0

o

_= ililliiiill • : f::^:.r:.f.:::ff f::::::: ^:

o

o Boo 1000 1500

2000

WAVENUMBER (cm-1)

Fig. 1. Accuracy of frequency calibration tables for selected molecules in

the 0-2000 cm-1 region.

2

W"

M

9

xs

Another prominent molecule in figure 1 is nitrous oxide and a large

amount of work has been completed on this molecule [7-9]. An interim calibra-

tion table exists for the 8 µm region but more work is needed and has been

planned for the future.

While these two molecules satisfy the five criteria above, there are

regions of the spectrum where these two molecules leave gaps in the coverage.

For example DBr covers some of the gap at 1800 cm-1 [10], but it does not meet

criterion #2. In DBr the spacing between calibration points is about 10 cm -1

and then only two markers appear (separated by about 0.2 cm-1 ) before another

10 cm-1 gap. Nonetheless, users have reported this to be quite useful.

The emphasis of the current work is to address the gap at 1500 cm-1 in

figure 1 and to provide references similar to that afforded by DBr. In

particular, we chose to provide markers every 7 to 10 cm-1 and also provide a

tunable diode laser (TDL) spectrum of the other lines in the vicinity to serve

as a signature.

Nitrogen dioxide does not meet the fourth criterion in that it 1s an

asymmetric rotor with spin split states and its Hamiltonian requires about 25

constants. Further, more than 3000 lines exist in the current Air Force

Geophysical Labs (AFGL) tables, and only one or two percent of these are

candidates for a heterodyne frequency measurement. Thus, our approach will

serve two purposes. First, it will provide frequency measurement based

calibration points with strongly absorbing lines in the gap region and serve

ab an interim calibration table. Second, our past experience with data from

different techniques indicates that while Fourier transform spectroscopic

(FTS) data are quite satisfactory for some requirements, there can sometimes

be a small calibration error. We suggest that the results from our study

either will be useful for the calibration of NO 2 in a FTS study, or serve as

an independent check of that work. We think that a measurement every 10 cm-1

or so will be satisfactory for this purpose. Figure 2 on the next page shows

a compressed FTS spectrum of nitrogen dioxide (the intense lines outside the

familiar P and R branch structure are H2 O lines) and the position of CO laser

lines which were used to make the heterodyne frequency measurements.

3

't

NITROGEN DIOXIDESPECTRA

0.90

0..10

0.50

0.3 0

0.10

1500. 1550. 600.

J^

700.

Positions of COlesser lines usedfor measurements

1500. 15 0. 16 0. 16 O. 1700. CM-1

Fig. 2. Overlap between nitrogen dioxide spectra and selected CO laser

lines.

EXPERIMENTAL TECHNIQUES

The measurement technique used for these measurements requires the use of

a CU laser to act as a. transfer oscillator. Its role is to transfer the

frequency synthesized from CO 2 laser frequency standards to the frequency of

the molecular feature of interest. Each of the frequency measurements of a

4

nitrogc . Li dioxide transition listed in Table I is a combination of two nearl;•

simultaneous measurements. The first one is a determination of the frequency

of a CO laser transition relative to the CO 2 laser standards. By the use of

two stabilized CO2 lasers, a metal-insulator-metal diode, and a microwave

oscillator, we generate a frequency, v., given by

vs — IV, + m32 + n3M , ( 1)

where v l and v2 are the frequencies of the CO 2 laser standards, and vM is a

microwave frequency. The quantities 1, m, and n are integers which are

allowed both positive and negative values. For these experiments, the value I

was always 3, and m was -1. The microwave frequencies are listed in Table I,

and the n value may be inferred since an X-band klystron was used. An rf beat

note vBl (the difference between the frequency v, and the CO laser frequency

vc o) was taken from the MIM diode, amplified and displayed on an rf Spectrum

analyzer where its center frequency was marked by an rf a ,rnthesizer. The

frequency of the transfer oscillator was then

"CO — Vxf.r — V. ± VBI' (2)

The second part of the measurement was a difference frequency measurement

between the CO laser transfer oscillator and a tunable diode laser whose

frequency was locked to the NO2 absorption feature of interest. This differ-

ence frequency beat note VB2 had its center frequency marked by a marker

oscillator whose frequency was counted and the frequency of the NO 2 transition

was then

VNO — Vxfer + VB2' (3)2

The measurements are given in Table I, which gives the CO 2 transitions

and the microwave frequency (in some cases a second harmonic is the value

shown) involved in each measurement, the frequency of the NO 2 transition along

with our estimated uncertainty and finally the quantum numbers assigned are

those taken from the AFGL tapes.

5

Tunable diode laser spectra in the vicinity of the each of the CO lase

lines used for the measurements are given in the appendix. These were

observed at a pressure of 113 Pa and a path length of 1.7 m. Differences

between the calculated frequency values in the AFGL tables and our heterodyne

measurements range from a few megahertz up to hundreds of megahertz for some

transitions.

For the heterodyne frequency measurements in Table I, the path length was

also 1.7 m. The pressure was reduced so tha.. for each transition measured the

absorption was in the linear regime. Typically, these pressures were in the

50 to 100 Pa range.

CONCLUSION

Since NO2 is an asymmetric rotor with spin split states and the majority

of the more than 3000 lines given in the AFGL tables are not close enough to

CO laser lines to permit heterodyne frequency measurements on them, we believe

the better approach is to measure only enough lines for the calibration and

l eave the detailed spectra for a FTS study. This will permit us to use our

resources to look at some N2 0 hot band features in the 1600 cm -1 region. This

represents something of a trade-off; a long path cell will be required for the

N2 0 spectra, but a marker every 0.5 cm -1 should be available. The greater

absorption afforded by NO2 will permit its use by all, but i-ntil a more

detailed study with a high resolution FTS instrument such as that accessible

to the JPL is complete, only a limited number of reference r oints will be

available.

ACKNOWLEDGMENT

We would like to thank Dr. J. Burkholder for taking some preliminary FTS

data on the local Bomen instrument of NOAA at our request. We also thank Dr.

D. A. Jennings for the use of his frequency synthesis programs. We are

grateful to Dr. A. Maki for his continuing cooperation and advice regarding

our frequency standards program. This work was supported in part by the Upper

Atmospheric Research Office of NASA.

6

REFERENCES

(1] Heterodyne Frequency Measurements with a Tunable Diode Laser CO 2 Laser

Spectrometer: Spectroscopic Reference Frequencies in the 9.5 Am Band of

Carbonyl Sulfide, J.S. Wells, F.R. Petersen and A.G. Maki, Appl. Opt. 18,

3567-3573 (1979).

[2] Heterodyne Frequency Measurements on the 11.6 Am Band of Carbonyl Sulfide

(OCS) and New Frequency/Wavelength Calibration Tables for both the 11.6

and 5.8 Am OCS Bands, Appl. Opt. 20, 1676-1684 (1980). Erratum: Appl.

Opt. 20, 2874 (1981).

[3] Heterodyne Frequency Measurements (at 11.6 Am) on Isotopic Species of

Carbonyl Sulfide, OC34 S, 013 CS, OC33 S, 18 0CS, and 013C34S, J.S. Wells,

F.R. Petersen, ti.G. Maki, and D.J. Sukle, J. Mol. Spectrosc. 89, 421-429

(1981).

(4] Heterodyne Frequency Measurements of Carbonyl Sulfide Transitions at 26

and 51 THz; Improved OCS, 0 13 CS, and OC 34 S Molecular Constants, J.S.

Wells, F.R. Petersen and A.G. Maki, J. Mol. Spectrosc. 98, 404-412

(1983).

[51 Heterodyne Frequency Measurements on the 12 0 0-001 0 Band of OCS, A.G.

Maki, J.S. Wells, and A. Hinz, Intl J. IR & MM Waves, 7, 909-917 (1986).

[6] Tables of Carbonyl Sulfide (OCS) Absorption Line Frequencies and Wave-

numbers for the Calibration of Tunable Infrared Lasers, A.G. Maki, J.S.

[Jells, F.R. Petersen, W.J. Lafferty, W.B. Olson, A. Fayt, and J.P.

Sattler, J. Phys. Chem. Ref. Data (in process).

[7] kbsolute Frequency Measurements of the 00 0 2-000 0, 20 0 1-000 0, and 1201-000

Bands of N2 0 by Heterodyne Speztroscopy, C.R. Pollock, F.R. Petersen,

D.A. Jennings, J.S. Wells, and A.G. Maki, J. Mol. Spectrosc. 107, 62-71

(1984).

(8] Heterodyne Frequency Measurements on N 2 0 at 5.3 and 9.0 Am, J.S. Wells,

D.A. Jennings, A. Hinz, J.S. Murray, and A.G. Maki, J. Opt. Soc. Am. B2,

857-861 (1985).

[9] Heterodyne Frequency Measurements on the 10 0 0-000 0 Band of N2 0 Near 8 Am,

J.S. Wells, A. Hinz, and A.G. Maki, J. Mol. Spectrosc. 114, 84-96 (1985).

(10] Heterodyne Measurements of Hot Bands and Isotopic Transitions of N2 0 near

7

1300 cm-1 , A. Hinz, J.S. Wells, and A.G. Maki, Atoms, Molecules, and

Clusters, (in press).

[11] Improved Deuterium Bromide 1-0 Band Molecular Constants from Heterodyne

Frequency Measurements, J.S. Wells, D.A. Jennings, and A.G. Maki, J. Mol.

Spectrosc. 107, 48-61 (1984).

8

APPENDIX

This appendix contains ten figures of nitrogen dioxide spectra in the

vicinity of the CO laser lines which were used in the heterodyne frequency

measurements. We have included them because we found the lower resolution

AFGL data to be somewhat difficult to reconcile with the higher resolution

TDL spectra. In some cases, this may have been due to less accurate line

poF'_tion data (calculated values in error due to poor constants) for example.

In other cases, perhaps it was simply a resolution problem. In any case, we

have found it preferable to have a signature at the resolution attainable by

the instrument at hand and, given the current status of the data (numerical

data not available at accuracy reported here), we feel spectral samples are

the interim answer.

Most of the spectra were recorded at a pressure of 113 Pa (0.85 torr) in

an absorption cell 1.7 m long. For the more intense regions of the spectra,

the pressure was reduced for the duration of a particular heterodyne frequency

measurement. The pressure was in general reduced to the linear absorption

regime and this afforded lines to be resolved that do not appear so in the

spectra shown (see Figs. A-4 and A-8 for example).

Three sets of numbers (given in cm-1 ) appear in the figures. The he*er-

odyne frequency measurements are given in square brackets with the uncertainty

in the last digits for the measurement given in parentheses with i n the

bracket, i.e., (1580.73450(33)). These numbers are positic ed on the page so

that the decimal point lines up above the center of the lin g that was mea-

sured, and in most cases they are placed above the spectra. A second set of

numbers comes from newly taken FTS data; in this case only the numbers to the

right of the decimal point are listed, except for a few obvious instances.

The FTS numbers are meant to supplement the frequency measurements and are

listed in parentheses. In some instances, these have been corrected where a

disagreement with heterodyne measurement seems to warrant it. Uncertainties

are not given for these measurements, but we believe that the values we list

are good to within 0.0005 cm-1 . The third set of numbers was taken from the

AFGL tables; these are positioned near the NO 2 spectra baseline and consist of

only the three significant digits listed in tie tables.

9

Fringes from a 7.5 cm germanium etalon were recorded below the NO 2 spectra.

Since the etalon was not temperature stabilized, these should nest be relied

upon for interpolation. We have used them only for line identification

purposes.

10

4

e

Table I. Heterodyne Frequency Measurements an Nitrogen Mod& with the Aid of a CO LaserTransfer oscillator.

_ Synthesis Scheme M laser NO2 Transition

002 trans.( 002 trans. IrW freq. trans. Prequencpa Quantum Mmbersfor 3v1 for -v2 MHz PV ., (J-') MHz J' Ka ' Kc' J" Ka" Kc" S-St

I636bP 22 I1626 P 32 24 200 P17(15) 49488134 . 4(90) 49 0 49 48 0 48 +

1636 P 18 II626 P 10 11 600 P18(11) 49190236 . 8(70) 37 4 33 36 4 32 -49190087.6(70) 37 4 33 36 4 32 +

I636 P 24 II626 P 20 7 500 P18(13) 48973387 . 0(70) 22 1 22 21 1 21 -48971356.7(90) 24 3 22 23 3 21 -48971185.8(90) 24 3 22 23 3 21 +48967881.8(70) 26 4 23 25 4 22 -48967623.7(70) 26 4 23 25 4 22 +

1636 P 24 II626 P 12 0 P18(15) 48758099 . 8(70) 19 5 14 18 5 13 -48752991.2(70) 22 6 17 21 6 16 -48749412.1(70) 14 3 12 13 3 11 -48748404.3(70) 16 4 13 15 4 12 +

I636 P 18 II626 R 16 -11 000 P19(10) 48555023 . 3(70) 21 8 13 20 8 12 +48551625.6(70) 10 5 6 9 5 5 -48550704.5(100) 13 6 7 12 6 6 -

I636 P 30 II626 P 10 22 000 P19(13) 48231914 . 6(50) 6 6 1 6 6 0 -48231205.7(50) 6 3 4 7 3 5 +48229667.9(50) 7 6 1 7 6 2 +48229360.7(50) 8 6 3 8 6 2 -48228499.0(100) 8 6 3 8 6 2 +48227145.8(100) 9 6 3 9 6 4 +48226313.4(50) 10 6 5 10 6 4 -48225637.6(50) 10 6 5 10 6 4 +

1636 P 22 II626 R 28 -10 000 P20(8) 48023593 . 6(70) 12 4 9 13 4 10 +48023320.2(70) 12 4 9 13 4 10 -48020088.1(70) 15 2 13 16 2 14 +48019774.1(70) 16 1 16 17 1 17 +48018936.9(70) 10 5 6 11 5 7 +48018294.6(70) 10 5 6 11 5 7 -

1636 P 36 II626 P 14 10 000 P20(10) 47817726 . 7(100) 21 3 18 22 3 19 . +

I636 P 28 II626 R 24 - 8 800 P20(12) 47605993 . 0(100) 16 8 9 17 8 10 +47605568.1(90) 16 8 9 17 8 10 -

I636 P 30 II626 R 26 -20 200 P20(14) 47394158 . 7(100) not assigned47389778.9(100) c 32 5 28 33 5 29 +47389452.2(100) 20 9 12 21 9 13 +47389228.2(100) 20 9 12 21 9 13 -

a) The uncertainty in the last digits is givp^ in parentb) The notation 626 and 636 refers to the s2C1602 and 13C1 isotopic lasers

respectively.c) We estimate xhat we locate the ma dmm point of this line to within 10 MHz,

however the line is blended, possibly with a water vapor line.

11

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*U.S. Government printing Otlloe: 1157-776 •S21/6511S zi

0NBSTedudcal Pubficadons

Jornnl of Rem—The Journal of Research of the National !emu of Standards reports NBS researchand development in those disciplines of the physical and engineering sciences in which the Banat is active.These include Physics, chemistry, cgineering, rnathanaWs, and computer sciences. Papers cover a broadrange of subjects, with major emphasis on meas<uanau methodology and the basic teduxAogy underlyingstandardisation. Also included from time to time are survey articles on topics closely related to the Bureau'stechnical and sc ifrc programs. Issued six times a year.

NonpaiodiaaLs

MaaopapM Major contributions to the tecirrtical literature on various subjects related to the Bureau's s=-tifrc and technical activities.1 1 2 n 1 1 3—Recommended codes of engineering and industrial practice (including safety codes) developed incooperation with interested industries, professional .xganizat}cins. and regulatory bodies.Spechd Pubicadons—Include proceedings of oonnferences snonsored by NBS. NBS annual reports, and otherspecial publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.Applied Matbemati s Series--Mathe natkal tables, manuals, and studies of special interest to physicists,engineers, chemists, biologists, mathematicians, computer p rogrammers, and others engaged in scientific andtechnical work.Nsdo nal Standard Reference Daly Series--Provides quantitative data on the physical and chemical propertiesof materials, compiled from the world's literature and critically evaluated. Developed under a worldwide pro-grain coordinated by NBS under the authority of the National Standard Data Act (Public Law 90-396).NOTE: The Journal of Physical and Chemical Refers nee Data (JPCRD) is published quarterly for NBS bythe American Chemical Society (ACS) and the Arrw can Institute of Physics (AIP). Subscriptions, reprints,and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.Building Science Series--Disseminates technical information developed at the Bureau on building materials,components, systems, and whole structures. The series presents research results, test methods, and perfor-mance criteria related to the structural and environmental functions and the durability and safetycharacteristics of building elements and systems.Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of asubject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subjectarea. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of othergovernment agencies.Voluntary Product Standards--Developed under procedures published by the Department of Commerce inFart 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized re-quirements for products, and provide all concerned interests with a basis for common understanding of thecharacteristics of the products. NBS administers this Grogram as a supplement to 6ic activities of the privatesector standardizing organizations.Consumer Information Series--Practical inlorrnation, based on NBS research and experience, covering areasof interest to the consumer. Easily understandable language and illustrations provide useful backgroundknowledge for shopping in today's technological marketplace.Order the abo,,e NBS publications from: Superintendent of Documents, Government Printing Office,Washington, DC _V402.Order the following NBS puh6cationcs—FIPS and ,'YBS/R's from the National Technical Information Ser-vice, Springfield, VA 22161.Federal Information Processing Standards Publications O WS PUW— Public-a:ions in this series collectivelyconstitute the Federal Information Processing Standards Register. The Register serves as the official source ofinformation in the Federal Govemment regarding standards issued by NBS pursuant to the Federal Propertyand Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat_ 1127), and as implementedby Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part of Title 15 CFR (Code of FederalRegulations).NBS Interagency Reports (NBSIW—A special series of interim or final reports on work performed by NBSfor outside sponsors (both government and non-government). In general, initial distribution is handled by thesponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161, in papercopy or microfiche form.