The objectives of the research are to measure low temperature laboratory rate coefficients for key reactions relevant to the atmospheres of Titan and Saturn. These reactions are, for example, C2H + H2, CH4, C2H2, and other hydrocarbons which need to be measured at low temperatures, down to approximately 150 K. The results of this work are provided to NASA specialists who study modeling of the hydrocarbon chemistry of the outer planets. The apparatus for this work consists of a pulsed laser photolysis system and a tunable F-center probe laser to monitor the disappearance of C2H. A low temperature cell with a cryogenic circulating fluid in the outer jacket provides the gas handling system for this work. These elements have been described in detail in previous reports. Several new results are completed and the publications are just being prepared. The reaction of C2H with C2H2 has been measured with an improved apparatus down to 154 K. An Arrhenius plot indicates a clear increase in the rate coefficient at the lowest temperatures, most likely because of the long-lived (C4H3) intermediate. The capability to achieve the lowest temperatures in this work was made possible by construction of a new cell and addition of a multipass arrangement for the probe laser, as well as improvements to the laser system

Leone, Stephen R.

English

NASA Technical Reports Server

CU Proposal No. 0995.08.1221B
NASA-CR-199435
Annual Status Report and
3rd Year Continuation Budget to the
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
SOLAR SYSTEM EXPLORATION DIVISION
OFFICE OF SPACE SCIENCE
DR. JAY BERGSTRALH, CODE SLC
NASA HEADQUARTERS
WASHINGTON, DC 20546
LABORATORY STUDIES OF LOW TEMPERATURE RATE COEFFICIENTS:
ATMOSPHERIC CHEMISTRY OF THE OUTER PLANETS
8
THE
Current NASA Grant:
Name and Address of Institution:
Research Area:
Date Submitted:
Starting Date and Duration:
NAGW-2438
The Regents of the
University of Colorado
Campus Box 19
Boulder, CO 80309-0019
Laboratory Measurements of
Chemical Kinetics, Planetary
Atmospheres Program
September 30, 1995
January 1,1996, 3rd year of grant
for 12 months
Amount:
Principal Investigator:
Authorizing Official:
ftien R. Leone, Fellow
JILA
University of Colorado
Boulder, CO 80309-0440
Telephone: (303)492-5128
Laurence D. Nelson, Director
Office of Contracts and Grants
Telephone: (303)492-6221
(NASA-CR-199435) LABORATORY N96-10866
STUDIES OF LOW TEMPERATURE RATE
COEFFICIENTS: THE ATMOSPHERIC
CHEMISTRY OF THE OUTER PLANETS Unclas
Annual Report, 1 Jan. - 30 Sep.
1995 (Colorado Univ.) 11 p
G3/91 0068084
https://ntrs.nasa.gov/search.jsp?R=19960000866 2020-06-16T06:46:10+00:00Z
CU -Proposal No. 0995.08.1221B
PROPOSED BUDGET
Institution: The Regents of the
University of Colorado
Campus Box 19
Boulder, CO 80309-0019
Principal Investigator: Stephen R. Leone
Title: Laboratory Studies of Low Temperature
Rate Coefficients: The Atmospheric
Chemistry of the Outer Planets
Duration: 1/1/96 -12/31/96
Salaries and Wages
Research Associates
To be named -12.00 Mo. @ $2333.33/Mo.
Fringe Benefits
Faculty and Research Associates
Insurance ($285/Mo.)
TIAA (9.00%), PICA (6.20%), Medicare (1.45%),
Wrk. Comp. (1.88%), Unemploy. (0.03%),
and Ann. Ins. (0.47%)
Total Fringe Benefits
Operating Expenses
Publication Charges
Supplies and Materials:
Infrared and UV optics
Spphire and quartz windows
Optical mounts
Liquid nitrogen ($.40/liq. liter)
Research compounds
Excimer laser gases
Infrared filters
Instrument Shop Charges @ $50.00/Hr.
(Exempt from Indirect Costs)
Total Operating Expenses
Travel
Domestic Travel
Total Direct Costs
Indirect Costs
On Campus: 43.5% of Modified Total Direct Costs,
predetermined for the period 7/1/94 - 6/30/96.
Per HHS agreement dated 10/20/93.
01/01/96
12/31/96
28,000
3,420
5,330
8,750
1,200
1,100
1,100
1,100
1,800
1,600
1,601
1,100
7,000
17,601
2,126
56,477
21,523
Total Annual Costs 78,000
Annual Status Report
1 January 1995 - 30 September 1995
The objectives of the research performed under NASA grant NAGW-2438 are
to measure low temperature laboratory rate coefficients for key reactions relevant to
the atmospheres of Titan and Saturn. These reactions are, for example, C2H + H2,
CH4, C2H2, and other hydrocarbons which need to be measured at low temperatures,
down to =150 K. The results of this work are provided to NASA specialists who
study modeling of the hydrocarbon chemistry of the outer planets. The apparatus
for this work consists of a pulsed laser photolysis system and a tunable F-center
probe laser to monitor the disappearance of C2H. A low temperature cell with a
cryogenic circulating fluid in the outer jacket provides the gas handling system for
this work. These elements have been described in detail in previous reports.
Several new results are completed and the publications are just being
prepared. The reaction of C2H with C2H2 has been measured with an improved
• ^ - • . . • ' . . ' * • r " :
apparatus down to 154 K.; Figure 1 shows the temperature dependence, which/
indicates a clear increase in the rate coefficient at the lowest temperatures, most
likely because of the long-lived [C4H3] intermediate. The fit to all the data in Fig. 1 is
k(T) = 8.6 x 10'16 T1'8 exp[(474±90)/T] cm3 molecule'1 s'1. The capability to achieve
the lowest temperatures in this work was made possible by construction of a new
cell and addition of a multipass arrangement for the probe laser, as well as
improvements to the laser system.
-21
ill
i
-23 -
-24
100000/T
Fig. 1. Arrhenius plot of C2H + C2H2. • recent results; o data from Pedersen,
Opansky, Leone J. Phys. Chem. 97, 6822 (1993).
The reaction studies of C2H + CH4 and CD4 have also been completed. Figure
2 shows an example of the observed rate of removal of C2H versus [CHJ and [CDJ at
359 K, which gives a good idea of the quality of the data.
0.7
0.6-
0.5 -
0.4 -
0.2 -
0.1 -
0.0
0.0 1.0 2.0
[CXJ (1011 nulecufc cm'1)
Fig. 2. Plot of observed pseudo first order rate of removal, kc»4= l/Tobterved, forC2H
versus [CH4] = o and [CDJ = •.
In Fig. 3 is shown an Arrhenius plot for the reactions of C2H with CH4 and
CD4. The best fits are k(T) = (1.2 ±0.1) x 10'11 exp[(-491±12)/T] for CH4 and (8.7±1.8) x
10'12 exp [-(650161 )/T], both in cm3 molecule"1 s'1. The results show a reasonably
large activation energy for these reactions and a large isotope effect (2.5±0.2) for
CH./CD4. There is no hint of curvature at the lowest temperatures, most likely
because the large activation energy dominates the reaction rate constants.
In a real tour de force experiment, the first low temperature rate coefficients
for C2H + H2 have now been obtained. Figure 4 shows these results along with
earlier higher temperature data. There is evidence for some curvature in this plot,
which may be indicative of quantum mechanical tunneling.
-26
C/3
ju
u
-27 -
I -28 H
-29 -
2.0 3.0 6.0 7.04.0 5.0
1000(K)/T
Fig. 3. Arrhenius plot of C2H + CH4 = o and CD4 = •.
1E
o
-25 -
-26 -
-27 -
-28 -
£ -29 -
-30-
-31
0.0
i
1.0 2.0 3.0 4.0
lOOO/TOC)'1
i
5.0
i
6.0 7.0
Fig. 4. Arrhenius plot for C2H + H2. • present results, D Koshi et al., J. Phys. Chem.
96,9839 (1992), o Glass et al., J. Phys. Chem. 97, 12789 (1993).
Planned Work
1 January 1996 - 31 December 1996
Immediate work to be pursued will be a study of the reaction rate coefficients
of C2H + ethane, propane, and butane at lower temperatures. The lower vapor
pressures of the larger hydrocarbons may limit the lower values of the temperature
that can be achieved with the present cell. There is very little work on the reactions
of C2H with nitrogen containing compounds, such as HCN, CH3CN, etc. Since the
coupling of the carbon chemistry and nitrogen chemistry is an important process in
the atmospheres of the outer planets, we intend to direct our studies along these
lines in the ear future. This will require a new kind of apparatus, to prevent
condensation of the nitrogen compounds on the walls of the flow cell. This work
will assess a new jet cooled laval nozzle to achieve even lower temperatures. Such
a method will necessitate multiphoton ionization or laser fluorescence schemes of
detection as well, and therefore part of our effort will be directed toward this goal.
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(GRANTS/COOPERATIVE AGREEMENTS)
A. The grantee certifies that it will provide a drug-free workplace by:
(a) Publishing a statement notifying employees that the unlawful manufacture,
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(b) Establishing a drug-free awareness program to inform employees about --
( 1 ) The dangers of drug abuse in the workplace;
(2) The grantee's policy of maintaining a drug-free workplace;
(3) Any available drug counseling, rehabilitation, and employee assistance
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(c) Making it a requirement that each employee to be engaged in the performance of the
grant be given a copy of the statement required by paragraph (a);
(d) Notifying the employee in the statement required by paragraph (a) that, as a
condition of employment under the grant, the employee will --
( 1 ) Abide by the terms of the statement, and
(2) Notify the employer of any criminal drug statute conviction for a violation
occurring in the workplace no later than five days after such conviction;
(e) Notifying the agency within ten days after receiving notice under subparagraph (d)
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subparagraph (d) (2), with respect to any employee who is so convicted ~
( 1 ) Taking appropriate personnel action against such an employee up to and
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(2) Requiring such employee to participate satisfactorily in a drug abuse
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Federal, State, or local health, law enforcement, or other appropriate
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(g) Making a good faith effort to continue to maintain a drug-free workplace through
implementation of paragraphs (a), (b), (c), (d), (e), and (f).
B . The grantee shall insert in the space provided below the site(s) for the performance of work
done in connection with the specific grant:
Place of Performance (Street address, city, county, state, zip code):
Universit of Colorado. Boulder. Colorado. 80309 _
Signature of Responsible University Official and Date:
Typed Name and Title:
Laurence D. Nelson. Director, Office of Contracts and Grants
Tide/Identification of Applicable Research Proposal:
Laboratory Studies of Low Temperature Rate Coefficients; The Atmospheric
Chemistry of the Outer Planets (Continuation of NAGW-2438)
NASA Proposal No.:
Laboratory Studies of Low Temperature Rate Coefficients: The Atmospheric
Title: Chemistry of the Outer Planets (Continuation of NAGW-2438)
Principal Investigators'): Stephen R. Leone
CERTIFICATION REGARDING DEBARMENT, SUSPENSION AND OTHER
RESPONSIBILITY MATTERS-PRIMARY COVERED TRANSACTIONS
(1) The prospective primary participant certifies to the best of its knowledge and belief, that it
and its principals:
(a) Are not presently debarred, suspended, proposed for debarment, declared
ineligible, or voluntarily excluded from covered transactions by any Federal
department or agency;
(b) Have not within a three-year period preceding this proposal been convicted of or
had a civil judgment rendered against them for commission of fraud or a criminal
offence in connection with obtaining, attempting to obtain, or performing a public
(Federal, State or local) transaction or contract under a public transaction; violation
of Federal or State antitrust statutes or commission of embezzlement, theft, forgery,
bribery, falsification or destruction of records, making false statements, or
receiving stolen property;
(c) Are not presently indicted for or otherwise criminally or civilly charged by a
governmental entity (Federal, State or local) with commission of any of the
offenses enumerated in paragraph (1) (b) of this certification; and
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more public transactions (Federal, State or local) terminated for cause or default.
(2) Where the prospective primary participant is unable to certify to any of the statements in
this certification, such prospective participant shall attach an explanation to this proposal.
CERTIFIED BY:
Signature Date
Laurence D. Nelson
Typed Name
Director. Office of Contracts and Grants
Title
University Qf Colorado at Boulder
Institution
Section 1352, Title 31, U.S.C. (PL 101-121, Section 319) entitled "Limitation on use of
appropriated funds to influence certain Federal contracting and financial transactions."
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Laurence D. Nelson, Director, Office of Contracts and Grants
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The Regents of the University of Colorado
Organization
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Grant/Modification No.
,
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Laboratory studies of low temperature rate coefficients: The atmospheric chemistry of the outer planets

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