The first interstellar hydrocarbon ring, cyclopropenylidene (C3H2) is being studied. Both a survey of galactic sources in several C3H2 transitions and a more detailed study of a subset of these sources are under way. In the latter category is a study of the nearby cold dark cloud TMC-1, which is a potential formation site for solar type stars. A spectra is shown of seven rotational transitions which have been observed at the Five College Radio Astronomy Observatory. Three of these were detected for the first time in any astronomical source: the 3 sub 30 to 2 sub 21 transition at 216 GHz, the 2 sub 21 to 1 sub 10 transition at 122 GHz, and the 1 sub 11 to 0 sub 00 transition at 52 GHz. From the data it is apparent that C3H2 is quite spacially extended in typical interstellar molecular clouds, and that at least in TMC-1 it is one of the most abundant organic molecules

Irvine, W. M.

Schloerb, F. P.

English

NASA Technical Reports Server

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DEPARTMENT OF PHYSICS AND ASTRONOMY
UNIVERSITY OF MASSACHUSETTS
NASA GRANT NAGW-436
BOUNDARY CONDITIONS FOR THE PALEOENVIRONMENT: CHEMICAL AND
PHYSICAL PROCESSES IN THE PRE-SOLAR NEBULA
SEMI-ANNUAL STATUS REPORT NO. 7
February 16, 1986 - August 15, 1986
a- : Principal Investigator: William M. Irvine
£! . . Co-Principal Investigator: F. Peter Schloerb
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: 2 Irvine and graduate student S. Madden, in collaboration with colleagues at
'.' H) • oo the Herzberg Institute of Astrophysics in Canada,- continued their study of the
•a? C7>Oi m o si...
£ vi ^ u first interstellar hydrocarbon ring, cyclopropenylidene (C H-). Both a
f a a! *~ U survey of galactic sources in several C,H. transitions and a more detailed
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' H a «a • study of a sub-set of these sources are under way. In the latter category is
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'•o ^  S ^ r^ . a study of the nearby cold dark cloud TMC-1, which is a potential formation
; >i 3 «j *" A site for solar-type stars. Figure 1 shows spectra of seven rotational transi-
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QUO ui -H tions which have been observed at the Five College Radio Astronomy Observatory.
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i ° a S « w T^ 1"66 °f these have been detected for the first time in any astronomical
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^§01 n u! source: the 3_/>-2_. transition at 216 GHz, the 2__-l,rt transition atoo!n2w 30 21 21 10
f" O US W "(0 3
; co M 4J x) 122 GHz, and the 1,,-0.,rt transition at 52 GHz. From the data it is
WS > SB LO O 11 00
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*"" K « ^ m apparent that C-H- is quite specially extended in typical interstellar
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•as w o e co organic molecules.
53 03 B? Q> 01
«-»H Pu CO r- •
Because it is apparent that many of the C.H. transitions observed in
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ORIGINAL -PASS-IS
OF POOR QUALITY
^H^ DETECTIONS
I N T M C - l
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_ L»
rv-v*-! ^wwj VIA^VL F*"*\\
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Figure J. — FCSAO observations of the ring molecule Cj^ in the dark cloud
TMC-l. First astronomical detections of the 330-221, 22i-lio» and lll"^00
The frequency versality of the 14m telescope system was critical to this
multi-transition study, which spans 46 tn 216 GHz.
cold clouds are strongly saturated, observations of rarer isotopic variants
are very important in order to establish the true opacity in these lines.
13This has recently become possible following the measurement of both C
variants in a molecular spectroscopy laboratory at Lille, France. Following
publication of the molecular constants, we have made the first detection of a
13C variant, as shown in Figure 2. Such detections allow estimates to be
made of the fractional abundance of the main isotopic variant in three inter-
stellar sources. As expected, C H is indeed one of the most abundant
organic constituents in the cold cloud TMC-1. It is about an order of
magnitude less abundant in the giant molecular cloud Sgr B2, located close to
the Galactic center. On the other hand, in the sources observed to date it is
most abundant in the envelope of the evolved carbon star IRC+10216. This
pattern of abundances is similar to that of the cyanopolyynes, suggesting that
the formation mechanisms for C^ H. may be related to that for linear carbon
chains.
The study of C.H. has also been pursued at other radio observatories
where that has been appropriate. For example, the facilities of the National
Radio Astronomy Observatory in Green Bank, West Virginia, have been used to
investigate the 2- -2 transition, which has the surprising property that
it is seen in absorption against the cosmic microwave background. This
implies that it is "refrigerated" below the universal 3 K background. Since
the excitation is thus very far from equilibrium, it seems likely that the
behavior of this transition may be a sensitive probe of physical conditions in
interstellar sources.
In a continuing study of the chemistry of the cold, quiescent dark clouds,
many of which may contain solar mass protostars or presolar nebula, Madden and
visiting Swedish astronomer P. Friberg have shown that methanol (CH OH) is
-2-
0.36
0.32
>-
(S)
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0.28
0.24
B
-200 0 200
VELOCITY (km/s)
Figure 2 — Spectrum of the Galactic center cloud Sgr B2 at 84 Ghz
showing emission due to 13-carbon substituted C.H. (A), CH_CHO (B), and
CH»CH_CN (C). Horizontal axis expresses frequency in terms of Doppler
velocity relative to the local standard_of rest, taking the rest frequency
of the observed ^ O^l transition of CCCH2 as 8A185-.629 .MHz.
widely distributed in such sources. Interestingly enough, this molecule
appears to be roughly equally abundant in all of the dark clouds surveyed,
unlike the cyanopolyynes, which exhibit very pronounced abundance variations
from source to source. In a related search for other oxygen-containing
organic molecules, dimethyl ether (CH.OCH.) was sought in the dark clouds
TMC-1 and L134N, and upper limits on its abundance were obtained.
In a collaboration with radio astronomers in France and at the NRAO, L.
Ziurys has made a tentative detection of a new interstellar ion, protonated
water (H-O*). Only one transition, at 307 GHz, has thus far been
detected, so that the assignment must be regarded as tentative until further
lines can be sought. Nonetheless, H,0 is an expected constituent of
interstellar clouds, and its detection would provide a way to estimate the
important abundance of water in these sources. The principal transitions of
water itself are in the submillimeter region and are blocked from observations
by the Earth's atmosphere.
In a collaboration with scientists from the University of Wisconsin,
Irvine and UMass astronomer R. Dickman have discovered another new inter-
stellar ion, SO . This,is an important addition to the interstellar
inventory, since the chemistry of sulfur-containing molecules in the inter-
stellar medium is a matter of considerable controversy. In particular, there
have been suggestions that the abundance of previously detected sulfur-
containing species cannot be well explained by existing gas phase models of
interstellar chemistry and may require production mechanisms involving the
particulate grains. The results of the SO observations are currently being
analyzed in order to address these questions.
The study of differences in the chemistry among interstellar clouds is
critical for determining the type of processes which take place and the degree
-3-
to which chemical evolution occurs as the clouds themselves evolve. Ziurys
has been using the FCRAO 14 meter antenna to study "high temperature"
chemistry in order to investigate possible differences with respect to that
in the cold, quiescent clouds. One approach to this problem is through
observations of vibrationally excited species. In order for vibrational
excitation to occur, molecules must be present in unusually hot and dense gas,
and/or where strong infrared radiation is present. Vibrational excitation
thus serves as a probe of physical conditions near star-forming regions and
traces material where shock or high temperature chemistry may be occurring.
Most recently the emission from vibrationally excited HCN has been mapped in
the core of the Orion Molecular Cloud at 267 GHz. The results show that the
emission arises from a region smaller than 20 arcseconds. Such a distribution
is consistent with the assumption that the molecules are located in the "hot
core" component of this cloud, and the abundance can be compared with that of
other constituents detected in this region.
A number of molecules containing second and third row elements from the
periodic table are thought to be formed from high temperature processes and/or
the destruction of interstellar grains. If the gas is sufficiently hot,
activation energy barriers in chemical reactions may be overcome, allowing
otherwise inaccessible reaction pathways to take place. Ziurys has been
continuing her study of SiO and SiS in this regard and appears to have
discovered a possible new protostar in the Orion Molecular Cloud. In addition
to these silicon-containing species, searches have been made for molecules
containing other second and third row elements, including MgO, CaOH, and PN.
Emission lines which may be assignable to PN have been detected in several
sources. There are also lines that may arise from CaOH, although positive
identification of this species awaits a better determination of laboratory
-4-
rest frequencies.
Irvine and Ziurys continue their efforts to identify a harmonically
related series of interstellar emission lines occurring in both the cold cloud
TMC-1 and in the giant molecular cloud Sgr B2. Stringent upper limits to
lines at intermediate frequencies have been obtained, so that the quantum
numbers of the observed transitions can now be specified. As a result, an
approximate rotational constant has been determined.
Schloerb and colleagues at the University of Massachusetts have continued
their study of the detailed structure of molecular material in regions of
active star formation. It is clear that the formation of both solar type and
more massive stars is typically accompanied by violent outflows of material
which can disrupt the surrounding ambient cloud, perhaps terminating the
process of star formation. Study of this process involves high spacial
resolution mapping of extended regions of such clouds, and recent efforts of
concentrated on the Orion Molecular Cloud.
Irvine presented invited reviews on interstellar chemistry at the COSPAR
meeting in Toulouse, France, in early July of this year, and a more extended
review at a Summer School on Interstellar Processes organized by the
University of Wyoming and the American Astronomical Society, also in July of
1986. Irvine also continues as Co-chairman of a series of NASA Workshops on
Exobiology in Earth Orbit and has been assisting in the editing of the
Workshop Report. Ziurys and Schloerb attended the Summer School on Inter-
stellar Processes in Wyoming and presented papers on research relevant to this
grant.
Papers supported by this grant and published during the period of this
report:
1. "Observations of the Hydrocarbon Ring 031*2", Matthews, H.E.
and Irvine, W.M., in Masers. Molecules and Mass Outflows in Star
-5-
Forming Regions. ed. A. Haschick (NEROC Haystack Obs.), pp. 1-8
(1986).
2. "Boundary Conditions for the Paleoenvironment: Chemical and Physical
Processes in Dense Interstellar Clouds", Irvine, W.M., Schloerb, F.P.
and Ziurys, L.M., in Second Symp. Chem. Evol. and Origin of Life.
NASA Conf. Publ. 2425, p. 42.
3. "Ammonia Masers Detected in Star-Forming Regions", Madden S.C.,
Irvine, W.M., Matthews, H.E., Brown, R.D., and Godfrey, P.D., in
Masers. Molecules and Mass Outflows in Star Forming Regions. ed.
A. Haschick (NEROC Haystack Obs.), pp. 289-298 (1986).
4. "HCNH+: A New Interstellar Molecular Ion", Ziurys, L.M., and Turner,
B.E., Ap.J. (Letters). 302. L31 (1986).
5. "New Detections of Interstellar Transient Molecules", Ziurys, L.M.,
and Turner, B.E., 17th International Symposium on Free Radicals and
other Transient Species, Granby, CO, August 1985.
6. "Vibrationally-Excited HCN in Orion-KL and IRC-H0216", Ziurys, L.M.,
and Turner, B.E., Molecules. Masers. and Mass Outflows in Star
Forming Regions. ed. A. Haschick (NEROC Haystack Obs.), pp. 23-30
(1986).
Research supported by this grant currently in press:
1. "Variations in the HCN/HNC Abundance Ratio in the Orion Molecular
Cloud", Goldsmith, P.F., Irvine, W.M., Hjalmarson, A., and Ellder,
J., Astrophys. J.. in press (1986).
2. "Studies of Organic Molecules Containing Methyl Groups in Dark Clouds",
Friberg, P., Irvine, W.M., Madden, S.C., Hjalmarson, A., in Astro-
chemistry (IAU Syrop. 120). ed. M.S. Vardya and S.P. Tarafdar (D.
Reidel), in press (1986).
3. "The Chemistry of Cold Dark Interstellar Clouds", Irvine, W.M., in
Astroehemistry (IAU Symp. 120). ed. M.S. Vardya and S.P. Tarafdar
(D. Reidel), in press (1986).
4. "Interstellar Molecules and Astroehemistry", Turner, B.E., and Ziurys,
L.M., in Galactic and Extragalaetic Radio Astronomy, ed. K. Keller-man
and G. Verschurr (Springer-Verlag: Berlin, Heidelberg, and New York),
submitted for publication.
5. "New Interstellar Detections: Implications for Shock Chemistry",
Ziurys, L.M., and Turner, B.E., Astrochemistry (IAU Symp. 120). ed.
S.P. Tarafdar and M.S. Vardya (Dordrecht: Reidel), in press.
6. "Observations of OCS and a Search for OC3S in the Interstellar Medium,
Matthews, H.E., MacLeod, J.M., Broten, N.W., Friberg, P. and Madden,
S.C., Astrophys.J._. in press (1986).
7. "Detections of 13C-Substituted 0^2 in Astronomical Sources",
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Madden, S.C., Irvine, W.M., and Matthews, H.E., Astrophys.J., submitted.
8. "Observational Astrochemistry", Irvine, W.M. and Hjalmarson, A., Adv.
Space Sci.. submitted.
9. "Chemical Abundances in Molecular Clouds", Irvine, W.M., Goldsmith,
P.F., and Hjalmarson, A. in Summer School on Interstellar Processes.
ed. D. Hollenbach and H. Thronson (Dordrecht: Reidel), in press.
10. "The C3H2 220~2n Transition: Absorption in Cold Dark Clouds",
Matthews, H.E., Madden, S.C., Avery, L.W. and Irvine, W.M., Astrophys.J.
(Letters), in press.
11. "A Search for Interstellar H30+, Wootten, A., Boulanger, F., Ziurys,
L.M., Bogey, M., Combes, F., Encrenaz, P., and Gerin, M., Astron.
Astrophys.. in press.
12. "Studies of Interstellar Vibrationally Excited Molecules", Ziurys, L.M.,
Snell, R.L., Erickson, N.R., and Turner, B.E., in Summer School on
Interstellar Processes, ed. D. Hollenbach and H. Thronson (Dorchecht:
Reidel), in press.
13. "Exobiology in Earth Orbit; Tarter, J., DeFrees, D., Brownlee, D.,
Usher, D., Klein, H.P., and Irvine, W.M., Fifth ISSOL Meeting.
Berkeley, CA., July, 1986.
14. "Multitransition Studies of C3H2", Madden, S.C., Irvine, W.M.,
Matthews, H.E. and Avery, L.M., in Summer School on Interstellar
Processes. ed. D. Hollenbach and H. Thronson (Dorchecht: Reidel),
in press.
Future Plans
Active research will continue on the abundance and distribution of
cyclopropenylidene in interstellar sources. Observing time has been granted
on the 100 meter telescope operated by the Max-Planck-Institut fur
Radioastronomie in Germany. This will enable high spacial resolution
observations of the strong 18 GHz transition to be made. In addition, the
ratio of the 18 to the 21 GHz transition, which is predicted to be an
indicator of density, will be studied in a variety of sources. Moreover,
there has recently been a laboratory measurement of the rotational frequencies
of deuterated CgH_, and we will attempt to detect this important isotopic
variant. Many other interstellar molecules show strong deuterium fraction-
-7-
ation, which can be used to investigate relevant reaction pathways. Further
13
observations of C-substituted C.H. will also continue including a
search for the less abundant (on-axis) variant.
Ziurys will continue to pursue radio astronomical studies of high
temperature chemistry through the detection and study of new interstellar
species, as well as observations of known molecules which are predicted to be
indicators of processes at elevated temperatures. Specifically, studies will
be carried out excited vibrational modes of HCO , N.H , and CS; of metal
containing species such as MgH, CaH, CaOH, and MgOH; and studies of additional
new molecular neutrals and ions.
Madden is continuing her studies of highly excited masing transitions of
ammonia in star forming regions. In an effort to determine the excitation
process for the maser lines, additional transitions will be sought. A
statistical equilibrium computer code is being developed to study the process
of molecular excitation.
The assignment of presently unidentified interstellar lines will be
continued through the search for related transitions and for satellite
structure. In addition, a spectral line survey in the 20 GHz band has been
allocated observing time at NRAO Green Bank and will be pursued by Irvine,
Ziurys, Madden, and colleagues in Sweden and Canada.
Several observing projects described under Current Research will continue
in order to better determine chemical abundances and relevant reaction
processes. For example, studies of additional SO transitions will be made,
efforts to detect additional lines of PN to confirm the tentative identifica-
tion will be pursued, and further observations in an attempt to confirm the
identification of H,0 will be undertaken. Likewise, Schloerb will
continue study of the structure and kinematics of nearby molecular clouds in
-8-
order to study the process of star and solar nebula formation, and the
resulting disruptive effects on the parental molecular clouds.
As a member of the Committee on Planetary Biology and Chemical Evolution
(NAS-HRC) Irvine will be jointly responsible for the preparation of a strategy
document for the study of Exobiology, which is being prepared for presentation
to the Space Science Board. Irvine has also been invited by the Rector of
Helsinki University to present an invited lecture on interstellar chemistry.
William M. Irvine
Principal Investigator
F. Peter Schloerb
Co-Principal Investigator
September 9, 1986
-9-


Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

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