S
upplementary
M
aterial
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Oxygen isotope equilibria of O
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bearing organic compounds based on first principle
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quantum mechanical models, and implications for their use in the study of extraterrestrial
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organics
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Surjyendu Bhattacharjee
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and John M. Eiler
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California Institute of Technology, 1200 E. California Blvd., Pasadena, CA
-
91125, USA
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1.
Factors influencing accuracy and precision of prediction
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1.
1
Basis set
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The choice of basis has a first order influence in calculation of vibrational frequency of a
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system.
Larger basis set renders more accurate
predictions
but
are also computationally
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demanding.
To evaluate the effect of basis set size on calculation of
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β
a
nd
k
; several systems
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have been investigated at both DZ and TZ level. Here we report two variables as measures of this
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difference:
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Δ
18
O
TZ
-
DZ
=
1000*ln[
18
β
TZ
/
18
β
DZ
]
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Δk
TZ
-
DZ
=
k
TZ
-
k
DZ
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Generally,
Δ
18
O
TZ
-
DZ
is small (<2 ‰
) and
within analytical uncertainty of previous experimental
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results for
the systems investigated
(
fig. S1b
).
Δ
18
O
TZ
-
DZ
values for C=O and C
-
O
-
H groups
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systematically differ from each other (1.23 ± 0.28 ‰ for C=O vs. 0.26 ± 0.38 ‰ for C
-
O
-
H at
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273K). The magnitude of this difference decreases as temperature increases. Average
Δk
TZ
-
DZ
for
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all systems considered is indistingu
ishable from
zero
(
fig. S1d
), within typical analytical
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uncertainties, and essentially constant with temperature.
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Figure S1
: Difference in
18
O/
16
O fractionation and mass laws for use of different basis sets and
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solvation models. (a)
Difference in
18
O/
16
O fractionation between cluster solvation and explicit
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solvation and its temperature dependence. (b) Difference in
18
O/
16
O fractionation between
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calculations using DZ and TZ basis set (error envelope 1σ). (c) Difference in k between cluster
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and explicit so
lvation. (d) Difference in k between DZ and TZ basis set (error envelope 1σ).
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