Chemistry Reference
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isomers with cumulated double bonds, (
)
n
, are almost exclu-
sively produced by carbon vapor condensation under laboratory conditions.
If so, it severely constrains finding natural carbynes because earth sciences
must adhere to the Principle of Actualism formulated by James Hutton
(1726-1797): ''No powers are to be employed that are not natural to the globe,
no action to be admitted except those of which we know the principle''. That is,
accepting that processes operating in Earth's past proceeded exactly as we
can observe them in action today. The second part of the original formu-
lation was amended to include experimental verification under controlled
conditions. Nowhere on Earth are carbynes or other pure carbons observed
condensing from a natural carbon vapor. Natural carbyne formation will
require some geologically acceptable process. When, indeed, carbynes could
only be produced in carbon-vapor condensation experiments [1], their for-
mation will be limited to environments conducive to carbon sublimation,
which, insofar as we know, would only be in astronomical environments [8]
whereof the physiochemical conditions and the gas and solid compositions
can only be probed by remote-sensing spectroscopic techniques.
The notion that polyynes could be common carbon dust around young
stellar objects (YSOs) that are believed to be in the process of forming
a planetary system, such as the solar nebula 4.57 Gyrs ago, is based on the
widespread occurrence of acetylene [H-(C
¼
C
¼
C
¼
C
¼
C)-H] as a parent gas for
carbyne condensation [9]. It is possible that carbynes could form by extra-
terrestrial carbon-vapor condensation. For the solar nebula we have an
opportunity to study such carbon dust in the laboratory using collected
extraterrestrial materials, viz. meteorites from asteroids and interplanetary
dust particles (IDPs) from comet nuclei and very primitive asteroids [10].
Earth scientists keep searching for alternative origins or interpretations than
condensation. For example, the basal layer thickness ranging from 0.489 nm
to 0.363 nm in a sample from the Sri Lanka (formerly Ceylon) graphite type
locality covers the full range of c
0
-values reported for carbynes. The layers
were interpreted as pre-graphitic carbon with variable admixtures of H, O,
and N that are not routinely determined in HRTEM studies [11,12];
certainly not when natural carbynes were first reported in the literature.
The main issue is that carbynes are metastable carbon crystals [13]
that:
1. Have no unique P,T constraints or formation modes, (a) flash-heating
and carbon vapor sublimation produced by resistive heating or
laser ablation using different starting materials (e.g. graphite,
glassy carbon), (b) impact compression [14-16] and (c) carbon-rich
vapor pyrolysis activated by electrons, ions and near-UV to IR
photons [17]
2. Are typically associated with other carbynes, graphite, cubic dia-
mond, amorphous carbon, in random, unpredictable combinations
[14, 16, 18-20]
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