The present of gas phase methanol in dense interstellar molecular clouds was established by radio detection of its rotational emission lines. However, the position, width, and profile of a absorption band near 1470 cm(exp -1) in the IR spectra of many dense molecular clouds strongly suggests that solid methanol is an important component of interstellar ices. In an attempt to better constrain the identification of 1470 cm(exp -1) feature, we began a program to search for other characteristic absorption bands of solid state methanol in the spectra of objects known to produce this band. One such feature is now identified in the spectra of several dense molecular clouds and its position, width, and profile fit well with those of laboratory H2O:CH3OH ices. Thus, the presence of methanol-bearing ices in space is confirmed

Allamandola, L. J.

Herbst, T.

Sandford, S. A.

Tielens, A. G. G. M.

English

NASA Technical Reports Server

54th MET SOC
N92- 12963
METHANOL IN THE SKY WITH DIAMONDS; L.J. Allamandola, S.A. Sandford,
A.G.G.M. Tielens, NASA/Ames Research Center, MS 245-6, Moffett Field, CA 94035, and
T. Herbst, Univ. of Hawaii, Institute for Astronomy, 2680 Woodlawn Dr., Honolulu, HI 96822
The presence of gas phase methanol (CH3OH) in dense interstellar molecular clouds was
established by the radio detection of its rotational emission Lines (1). The presence of solid state
methanol in these clouds had not been as rigorously demonstrated (2). However, the position,
width, and profile of an absorption band near 1470 cm -1 (6.8 lam) in the infrared spectra of many
dense molecular clouds strongly suggests that solid methanol is an important component of
interstellar ices. This identification of the 1470 cm -1 (6.8/am) band is not unique, however, and
other identifications of the feature have been suggested (3). In an attempt to better constrain the
identification of the 1470 cm -1 (6.8 _tm) feature we began a program to search for other
characteristic absorption bands of solid state methanol in the spectra of objects known to produce
the 1470 cm -1 (6.8 lam) band. One such feature has now been unambiguously identified in the
spectra of several dense molecular clouds and its position, width, and profile fit well with those of
laboratory H20:CH3OH ices. Thus, the presence of methanol-bearing ices in space is confirmed.
In all the spectra in which the new methanol band was detected, and in several spectra in which
the feature was not detected, a second, unexpected band was discovered. After consideration of
the position, width, and profile of the new band we tentatively identify micro-diamonds to be the
source material causing the new absorption feature. The identification of the absorption feature
with micro-diamonds is supported by comparisons with spectra from vapor-condensed micro-
diamonds studied in the laboratory. There are indications that this material is ubiquitous in space
and it is therefore likely to be related to the meteoritic diamonds that carry interstellar signatures
(4).
The abundances of thesetwo importantC-bearingmaterials,theimplicationsof theirdetection
in space,and therelationshipof thesediamonds tothoseidentifiedin meteoriteswillbe discussed
infurtherdetailinthe talk.
Reference_:
(1) cf. Irvine, W.M., Goldsmith, D.F., and Hjalmarson, A. (1987), in InterstellitT Processes,
eds. D. Hollenbach and H. Thronson, D. Reidel, 561-609.
(2) Allamandola, L.L (1984), in Galactic and Extragalactic Infrared S_oectroscopy, eds. M.F.
Kessler and J.P. Phillips, Reidel, 5-35.
(3) Tielens, A.G.G.M. and Allamandola, L.J. (1987), in Physical Processes in Interstellar
1Q.LQ.¢._,eds. G. Morfd and M. Scholer, Reidel, 333'376.
(4) Lewis, R.S., Tang, M., Wacker, J.F., Anders, E., and Steel, E. (1987), _ 326,
160-162.
https://ntrs.nasa.gov/search.jsp?R=19920003685 2020-03-17T14:03:44+00:00Z
54th MET SOC 7
SIMS ANALYSIS OF MICROMETEOROID IMPACTS ON LDEF; S. Amari 1,
J. Foote 1, E. K. Jessberger 2, C. Simon 1, F. Stadermann 2, P. Swan 1, R. M. Walker 1 and E.
Zinner 1, 1McDonnell Center for the Space Sciences and Physics Dept., Washington University,
One Brookings Drive, St. Louis, MO 63132, 2Max-Planck-Institut fiir Kernphysik, Postfach
103980, D6900, Heidelberg, Germany.
LDEF experiment AO187-2 consisted of 237 capture cells, 120 on the leading edge, the
rest on the trailing edge. In each cell a 2 l.tm plastic foil, metallized on both sides, covered polished
Ge targets. Although all plastic covers except for 12 cells on the wailing edge failed during flight,
the Ge plates contain many extended impact features that were apparently produced by projectile
material that had penetrated the plastic foils while they were still intact. We optically scanned all
cells without plastic foil from the trailing edge and found extended impact features from 200 to
4000 Ixm in diameter with 4 characteristic morphologies: a. craters surrounded by deposits, b.
ring-shaped features, c. sprays, and d. "spider webs." 53 impacts were selected as high priority
candidates for ion probe analysis. After detailed documentation in the SEM impacts were analyzed
in the ion microprobe for the chemical composition of the remaining projectile material. Prior
simulation studies [1] had shown that extended impact on the Ge plates contained sufficient
projectile material for chemical and isotopic analysis by SIMS. We made multi-element point
analyses in lateral scans across the impact features. Each point analysis consisted of depth profiles
of a number of elements. In all of 12 impacts so far studied we found evidence for the presence of
projectile material in the form of elemental enhancements in the impact region, in 5 cases significant
amounts of projectile material were detected. One such analysis is shown in Figs. 1 and 2. Fig. 1
shows ion signals of different isotopes normalized to the 76Ge signal for a scan across a "spider
web" impact. In Fig. 2 the selected signals of 27A1, 28Si, 40Ca, 48Ti and 56Fe were normalized
with relative sensitivity factors determined from laboratory studies [1] to obtain elemental
abundance ratios relative to Mg. Their abundances indicate an extraterrestrial origin except for Si,
which is anomalously high and is probably dominated by contamination from RTV glue used to
bond the Ge plates to the A1 substrate. Enough material is present to allow isotopic measurements,
which will be reported at the meeting.
[1] Lange G. et al. (1986) Lunar Planet. Sci. XVII, 456.
10'[ " - "O I 103_
l°'[ ,.tio-'t :'al
_Ni Ii-'-='"TaI
10-5[ 10"2
0 100 200 300 400 500 0 100 200 300 400 500
Distance (gm) Distance (I.tm)
--W-AttMg[
--.-s_Ig I
-----Ca/Mg I
--o--Ti/Mg ]
---n--Fe/MgJ
8 54th MET SOC
Ca, Ti AND Sm ISOTOPIC COMPOSITIONS OF FINE-GRAINED
INTERSTELLAR SiC; S. Amari 1,2, E. Zinner 1 and R. Lewis 2, 1McDonnell Center for the
Space Sciences and the Physics Dept., Washington University, One Brookings Drive, Saint Louis,
MO 63130-4899 USA, 2 Enrico Fermi Institute, University of Chicago, 5630 S. Ellis Ave.,
Chicago, IL 60637-1433 USA.
We have extended ion probe isotopic measurements in fine-grained aggregates (-"bulk")
of SiC from C, N, Si, Mg, Ba and Nd [1, 2] to Ca, Ti, Cr, Fe and Sin. Measurements were
made on grain size fraction KJB (nominal size 0.1-0.2 _m) from the Murchison carbonaceous
chondrite [3] . We used high mass resolving power for all elements except Sm which was
analyzed (together with Ba and Nd) under energy filtering conditions. The results for Ca and Ti
shown in Figs. 1 and 2 are averages of 16 measurements on different aggregates. The Ti pattern
agrees better with the predictions for the He-burning shell of AGB stars [4] than the patterns
obtained for large single grains [5]. The AGB model predicts a proportionately (relative to 42Ca
and 43Ca) much smaller 44Ca excess than what is actually observed (Fig. 2). This excess is
probably due to the presence of rare exotic (---X) SiC grains carrying large 44Ca excesses [6] due
to the decay of 44Ti (tl/2 = 47 years). This is indicated by large variations (from 20 %o to 160 %0)
of the 44Ca excesses for different measurements, similar to the large variations of 26A1/27A1 (grains
X have a ratio of ~ 0.2 [6] ) previously seen in "bulk" measurements of different grain size
fractions [1] . The 53Cr/52Cr and 54Fe/56Fe ratios are normal within measurement errors.
However, the concentrations of Ca and Fe are surprisingly high and it is likely that these two
elements reside not in SiC but in other phases such as chromium spinels.
The isotopic measurements of Sm are complicated by the presence of isobaric interferences
from Nd and Gd. We have measured masses 147, 148 and 149 and corrected for 148Nd (a pure
r-process nuclide). This cannot be done exactly since we do not know the composition of pure s-
process Nd. An estimate was made by measuring the 135Ba/136Ba ratio and assuming the same s-
process to normal _xing ratio for Ba and Nd. The Sm ratios are plotted in Fig. 3 with errors for
148Sm/147Sm that reflect the extremes of the estimated s-process Nd composition. They display an
s-process signature, similar to Ba and Nd, which
agrees reasonably well with theoretical predictions [7]. so.
References: [1] Amari et al. (1991) Lunar Planet. _ 4o.Sci. XXII, 19; [2] Zinner et al. (1991) Lunar ..,
Planet. Sci. XXII, 1553; [3] Lewis et al. (1990) ,_. 3o.
Nature 348, 293; [4] Gallino et al.(1991) personal r..) 2o
communication; [5] Ireland et al. (1991) Ap. J.
(Lett) , in press; [6] Zinner et al. (1991) this ._ 10
volume; [7] K/_ppeler et al. (1989) Rep. Prog. Phys. _o o
52, 945.
.10
• Murchlson SIC KJB _T_
[] AGB.He shell + $00 _"
Fig. I
40 42 43 44
Isotopic Mass
60 , 400.
5040
N_
._, lO
0
300
2OO
I00
%0
-100
r._ -200
"_" -300¢,0
-400
0
Murchison SIC KJB AAGB He shell ÷ 200 F_
;Ig v
Fig. 2
46 47 48 49
Isotopic Mass
-I0
• Murchlson SIC l
'i
o Kippeler et al.
/
Fig. 3
lobo 2060 30bo 40bo 50o0
8 ('SmP'_Sm) _Yoo)
54th MET SOC 9
RENAZZO-LIKE CHONDRITES; A LIGHT ELEMENT STABLE ISOTOPE
STUDY; R.D. Ash, M.M. Grady, A.D. Morse and C.T. Pillinger, Planetary Science Unit,
Dept. of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, England.
Several meteorites from the Western Saharan desert have been likened, upon petrologic
grounds, to the carbonaceous chondrite Renazzo. Renazzo has distinctive light element stable
isotope signatures, with enrichments in deuterium and heavy nitrogen (1,2). Stepped combustion
of the meteorite shows that the release prof'de of the carbon and the composition of its component
parts are also quite unusual, although the bulk carbon isotopic signature is quite typical for
carbonaceous chondrites. EET 87770, another CR, has similar isotopic properties, deuterium and
15N enrichment (3).
The examined Saharan meteorites, a single find - El Djouf - and three specimens, found
500km to the north east, in close proximity to each other (Acfer 59, Acfer 139 and Acfer 186)
were analysed to determine their carbon, nitrogen and hydrogen contents and isotopic
compositions, along with Renazzo and EET 87770 for comparison.
The nitrogen stepped combustion analysis of E1 Djouf is very similar to that of EET 87770,
with two yield maxima, between 400" and 600°C and between 650 ° and 900°C with a 815N
between +120 and +180%o. Above 1000°C the 515N drops sharply, reaching minima of +22%0 in
EET 87770 and -213°/_ in E1 Djouf. This component, absent from Renazzo, may be due to
presolar SiC which is 14N enriched (4). Such a light 515N in a whole rock sample implies that it
is present in unprecedented concentrations. The three Acfer 'CRs', analysed by single step
combustion, showed lower 515N values than the other CRs, lying between +65%0 and +103_'_
compared with E1 Djouf (+119_) and Renazzo and EET 87770 (+163 and +158%o respectively).
The carbon isotopic compositions of the meteorites lie within the field of all carbonaceous
chondrites, with 513C values between -5.0 and -12%o. Stepped combustion analysis may give
more unequivocal results, with Renazzo showing three distinct isotopic peaks, including a heavy
carbon component (+40_) combusting at high temperature.
The D/I-I signatures of the Saharan meteorites were unlike those of either Renazzo (+547 to
+1054°/_) or EET 87770 (+1309_), with E1 Djouf showing a light isotopic composition (-71 to
-159%o) and the Acfer samples a maximum enrichment in deuterium of up to +172%o.
Thus there are several isotopic similarities between the CRs and these desert meteorites, but
the D/H ratios differ, whether due primary differences or to isotopic exchange during terrestrial
weathering is unclear.
(1) Kolodny et al., (1980) E.P.S.L. 46, 149-158. (2) Kung & Clayton (1978) E.P.S.L.
38, 421-435. (3) Grady et al., (1991) L.P.S.C. XXII, 471-472 (4) Ash et al., (1989)
Meteoritics 22, 248-249.


Methanol in the sky with diamonds

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