Transcript Silane OSU talk.pptx

Structural studies of CH3SiF2-X (X = NCO, Cl) by
microwave spectroscopy
Gamil A. Guirgis, Jason S. Overby
College of Charleston
Nathan A. Seifert, Daniel P. Zaleski, Brooks H. Pate
University of Virginia
Michael H. Palmer
University of Edinburgh
Rebecca A. Peebles, Sean A. Peebles, Lena F. Elmuti, Daniel A. Obenchain
Eastern Illinois University
Introduction:
CH3SiF2NCO
• Simple molecules of the isocyanate and related classes, such as CH3NCO and CH3NCS
show extremely non-rigid behavior due to both low-lying torsional and C-NCO bending modes
• First excited state of CNC bend for CH3NCO is only 200 cm-1 + anharmonic potential
• CH3 barrier to rotation at equilibrium is small, only ~21 cm-1
• Traditional semi-rigid rotor fit can only fit K = 0 for low J 1
• Most recent model Hamiltonian fit only gets RMS to 3.0 MHz with data up to 40 GHz! (Jmax = 3) 2
• Similar silanes, such as H3SiNCO3 and HF2SiNCO4 (RC10, 2010),
can be fit using a typical Watson semi-rigid Hamiltonian,
but exhibit abnormally large distortion constants.
• H3SiNCO: DJK = 642.0(3) kHz; HF2SiNCO: ΔJK = 455.44(25) kHz
• For comparison, acetyl isocyanate: DJK = 8.6492 kHz 5
• Where does CH3F2SiNCO fall in terms of rigidity?
1.
2.
3.
4.
5.
R. G. Lett, W. H. Flygare, J. Chem. Phys. 47 (1967) 4730.
J. Koput. J. Mol. Spectrosc. 115 (1986) 131.
J.A. Duckett, A. G. Robiette, M. C. L. Gerry, J. Mol. Spectrosc. 90 (1981) 374.
G. A. Guirgis, et al. J. Mol. Struct. 983 (2010) 5.
B. M. Landsberg, K. Iqbal. J. C. S. Faraday II. 76 (1980) 1208.
Introduction:
CH3SiF2Cl
•
Detected as impurity from isocyanate synthesis (see next slide for details)
• Provides a good comparison point for various
other structural studies of halogenated silanes and hydrocarbons:
• Naturally, CH3SiF2Cl
should be an intermediate
case in both rotor barrier
and structural
parameters.
• Isocyanate is often called
a “pseudohalogen”.
How does it compare
to the chloride analogue?
V3 /cm-1
C-Si / C-C /Å
(CH3)2SiH2
576.4
1.867(2)
L. Pierce, J. Chem. Phys. 34 (1961) 498.
CH3SiH2Cl
644
1.849(5)
R. H. Schwendeman, G.D. Jacobs, J. Chem. Phys. 36 (1962) 1251.
CH3SiHCl2
731
--
CH3SiCl3
875
1.848
CH3SiH2F
545(1)
1.849(5)
L.C. Krisher, L. Pierce, J. Chem. Phys. 32 (1960) 1619
CH3SiHF2
439(10)
1.840(1)
L.C. Krisher, L. Pierce, J. Chem. Phys. 32 (1960) 1619
413.994(9)
1.812(14)
J.R. Durig, Y.S. Li, C.C. Tong, J. Mol. Struct. 14 (1972) 255.
?
?
?
?
Species
CH3SiF3
CH3SiF2NCO
CH3SiF2Cl
Ref.
J. R. Durig, C. W. Hawley, J. Chem. Phys. 59 (1973) 1
M. A. Qtaitat, et al., Spectrochim. Acta A, 50 (1994) 621.
This work.
This work.
Experimental
•
Initial isocyanate spectroscopy performed at Eastern Illinois University
• Spectra taken on 480 MHz CP-FTMW and Balle-Flygare cavity
• CH3SiF2NCO was prepared by the reaction of
MeSiCl3 with AgOCN to form MeSiCl2NCO,
which was then fluorinated using SbF3 to form the
desired product.
Isotopologue measurements performed at UVa:
• 6.5-18 GHz arrangement6 (right), 400 000 avg
spectrum.
• CH3SiF2Cl was detected in the microwave spectrum,
likely as a fluorination byproduct (NCO is
halogen-like in its reactivity)
• Spectrum was taken using approximately a 0.2%
concentration of product vapor pressurized to 7 atm in Ne.
6. Brown, G. G.; Dian, B.C.; Douglass, K. O.; Geyer, S. M.; Shipman, S. T.; Pate, B. H. Rev. Sci. Instru. 2008, 79, 053103.
Results –
CH3SiF2NCO
High barrier methyl rotor
• No excited vibrational states observed
• SiNC bending mode calculated to be
380 cm-1
Some B-type Ka = 2 E state lines missing
• Remaining satellites fit as E-state
forbidden c-type transitions
Very near prolate (κ = –0.98) so
when asymmetry splitting ≃ A-E splitting,
K state mixing occurs between asymmetry
and torsional interactions
• Analyzed in detail
in ethanol by Pearson et al. a)
Parameter
Experimental
Ab initio
A / MHz
3827.347(7)
3778.6925
B / MHz
1264.5067(14)
1248.7872
C / MHz
1240.6182(11)
1225.0426
DJ / kHz
0.50(6)
0.42365
DK / kHz
-67.3(13)
-11.7087
DJK / kHz
65.4(3)
15.6186
dJ / kHz
-0.07(3)
0.0691
V3 / cm-1
446(50)
440
θα / °
58.0(8)
56
χaa /MHz
1.896(7)
2.0364
χbb-χcc /MHz
0.056(12)
0.0865
Δνrms / kHz
9.0
--
N
70
--
ma / mb (D)
--
1.474 / 2.179
13C-1
13C-2
29Si
30Si
15N
18O
A / MHz
3757.981(10)
3826.632(18)
3827.3801(58)
3827.4360(80)
3823.619(21)
3827.643(41)
B / MHz
1255.1750(18) 1251.1370(17) 1262.7308(11) 1260.9920(10) 1262.1399(27) 1202.9838(87)
C / MHz
1224.3390(19) 1227.6773(21)
1238.9109(8)
1237.2308(13) 1238.1686(23) 1181.4424(68)
N
17
20
40
38
13
8
Dnrms / kHz
26.9
24.9
20.4
17.7
21.5
27.3
a) J.C.
Pearson, K. V. L. N. Sastry, M. Winnewisser, E.
Herbst, F. C. De Lucia. J. Chem. Phys. Ref. Data. 1995,
24, 1.
Results –
C
Isotopologues
13
30Si
29Si
15N
r0
Results –
Isocyanate Structure
Parameter
rs /Å
r0 /Å
Ab-initio
r[H-C]
--
1.092*
1.092
r[C-Si]
1.951(2)
1.814(5)
1.831
r[N-Si]
1.453(7)
1.667(21)
1.693
r[N=C]
1.262(6)
1.205(25)
1.205
r[C=O]
1.164(2)
1.152(5)
1.116
r[F-Si]
--
1.57646(8)
1.586
∠[C-Si-N]
111.7(3)
111.3(5)
111.5
∠[Si-N-C]
156(2)
159.8(9)
157.4
rs
r0 structure fit with Kisiel’s STRFIT
Fluorine positions fit with Pcc instead of C
Imaginary coordinates in Kraitchman analysis
rs coordinates
r0 coordinates
CCSD(T)/6-311G++(3df,3pd)
|a|
|b|
a
b
a
b
C-1
1.7178(7)b)
1.5834(5)
-1.7215
-1.5660
-1.8345
-1.5237
C-2
2.0741(17)
0.1600(4)
2.0765
-0.1441
2.0768
-0.1857
O
3.2269(9)
[0.000]c)
3.2206
-0.0094
3.2341
0.00497
N
0.828(6)
0.362(4)
0.8885
-0.3431
0.8939
-0.4546
29Si
0.536(5)
[0.000]
-0.7496
-0.0338
-0.7579
-0.0405
30Si
0.621(3)
[0.000]
-
-
-
-
Ab Initio Results
Polynomial fit suggests
potential 2nd minimum;
likely to relax to global min.
in expansion.
157.4°
Attempts at a full relaxed SiNC PES
were not successful here at UVa.
Inspection of broadband spectrum
does not immediately suggest the existence
of a second conformer spectrum
Parameter
Experimental
Ab initio
A / MHz
3780.570(6)
3703.0901
B / MHz
2423.8177(16)
2380.5341
C / MHz
2317.9254(13)
2283.7826
DJ / kHz
0.668(55)
0.328
DK / kHz
2.36(32)
1.53
DJK / kHz
2.8(13)
0.602
dJ / kHz
--
--
V3 / cm-1
468(3)
435.835
θa / °
61.7(11)
55.004
χaa /MHz
-36.05(10)
-36.626
χbb-χcc /MHz
0.552(23)
0.5837
Δνrms / kHz
18.3
--
ma (D)
--
0.689
mb (D)
--
2.411
Results –
CH3SiF2Cl
Ka = 2 b-type E-state lines also disappear,
but no new c-type transitions were observed
• Less prolate than isocyanate (κ = –0.85)
 Weaker mixing?
High sensitivity (1500:1 S/N on strongest transition)
enabled detection of double silicon/chloride isotopologues
13C
37Cl
29Si
30Si
29Si
/ 37Cl
30Si
/ 37Cl
A / MHz
3703.550(34)
3780.135(134)
3780.638(17)
3780.695(25)
3780.200(5)
3780.257(6)
B / MHz
2408.968(25)
2362.405(6)
2422.381(11)
2420.985(14)
2360.820(2)
2359.262(3)
C / MHz
2275.425(13)
2261.532(6)
2316.623(13)
2315.327(13)
2260.075(2)
2258.647(3)
N
25
139
61
48
32
24
Dnrms / kHz
18.3
15.3
14.8
19.6
20.2
21.0
Results –
C
Isotopologues
13
29Si
30Si
212-101
37Cl
Results –
CH3SiF2Cl
Analysis identical to isocyanate
Structure in excellent agreement with
MP2/6-311G++(d,p) ab initio structure.
Small difference between
Ab-initio and rs / r0 values of the
rotor angles; suggests rotor tilt
due to Cl σ donation into the anti
methyl hydrogen
r[Si-C]/Å
r[Si-F]/Å
r[Si-Cl]/Å
∠[H-C-H]
∠[H-C-Si]
∠[F-Si-F]
∠[C-Si-Cl]
∠[F-Si-Cl]
rs
1.817(2)
-2.019(5)
---112.4(5)
--
r0 A,B,C
1.81(2)
1.58(1)
2.025(5)
--105.2(8)
113.1(7)
106(1)
Imaginary coordinates for Kraitchman,
but errors are less apparent in derived quantities than seen in -NCO
r0 A,B,Pcc
1.814(9)
1.5825(7)
2.027(3)
--106.0(5)
112.9(4)
106.0(6)
Results
V3 /cm-1
C-Si / C-C /Å
(CH3)2SiH2
576.4
1.867(2)
L. Pierce, J. Chem. Phys. 34 (1961) 498.
CH3SiH2Cl
644
1.849(5)
R. H. Schwendeman, G.D. Jacobs, J. Chem. Phys. 36 (1962) 1251.
CH3SiHCl2
731
--
CH3SiCl3
875
1.848
CH3SiH2F
545(1)
1.849(5)
CH3SiHF2
439(10)
1.840(1)
413.994(9)
1.812(14)
J. R. Durig, C. W. Hawley, J. Chem. Phys. 59 (1973) 1
M. A. Qtaitat, et al., Spectrochim. Acta A, 50 (1994) 621.
L.C. Krisher, L. Pierce, J. Chem. Phys. 32 (1960) 1619
L.C. Krisher, L. Pierce, J. Chem. Phys. 32 (1960) 1619
J.R. Durig, Y.S. Li, C.C. Tong, J. Mol. Struct. 14 (1972) 255.
Species
CH3SiF3
Ref.
CH3CH2F
1157
1.533(5)
CH3CHF2
1113
1.530(2)
B. Bak, et al. Spectrochim. Acta 16 (1960) 376.
R. G. Lerner, B. P. Dailey, J. Chem. Phys. 16 (1957) 678.
CH3CH2Cl
1290
1.520(3)
R. H. Schwendeman, G.D. Jacobs, J. Chem. Phys. 36 (1962) 1245.
CH3CHCl2
--
1.517(3)
W.H. Flygare, J. Mol. Spectrosc. 14 (1964) 145.
CH3SiF2NCO
446(50)
1.814(5)
This work.
CH3SiF2Cl
468(3)
1.814(0)
This work.
Conclusions
& Future Work
• Substitution and r0 structures for
CH3SiF2Cl and CH3SiF2NCO were determined
in natural abundance using CP-FTMW spectroscopy
• Internal rotation and nuclear hyperfine parameters
were fit, for a total global fit with an RMS of 9.0 and
18.3 kHz for the isocyanate and chloride normal species,
respectively.
• Addition of heavy atoms (fluorines) to the C-Si-NCO frame seem to ease the large-amplitude motions
and centrifugal distortion seen in other isocyanates.
•
Structural results from this study lend additional evidence to the pseudohalogen nature of the isocyanate group.
Future implications:
• With proper sensitivity measurements and sufficient sensitivity, substitution structures in natural abundance
become a routine process for a given molecule of interest.
•
Reaction product analysis for volatile mixtures.
• Ablation source  product analysis even for solid product mixtures?
Thank you for listening!
This work was supported by the National Science Foundation MRI-R2 project (0960074).
CH3NCO
• Koput’s fit
accounts for transitions
up to J = 3, with vbend between
0 and 3 and |m| ≤ 7 (torsional
level)
“Close coincidences of some CNC
bending-torsion-rotation
energy levels give rise to strong
accidental resonances
and some lines have been
observed to
be shifted as much as
several GHz (!) away
from the main bunches.”
Results –
Internal Rotation
• Used the program XIAM6 to simultaneously fit internal rotation and nuclear quadrupole
effects
• XIAM uses a “Combined Axis Method” (CAM) to fit the internal rotation; simply:
• Generates traditional Principal Axis Hamiltonian for system
• Rotates PA Hamiltonian into the rho-axis system:
• Rotates system into regime where the Coriolis cross terms disappear
• Rho-axis roughly collinear with rotor axis in PA system (only exactly true
with a symmetric top)
• Diagonalizes rho-axis Hamiltonian
• Rotates eigenvalues back to PA
• Advantages: Very fast for systems with sufficiently high barriers: only need to fit
A, B, C, V3, F and the rotor angle defined in PAM. Also, rotational constants
are equivalent to a standard PAM fit with an averaged line center between the A/E states.
6. H. Hartwig, H. Dreizler, Z. Naturforsch 51a (1996) 923.
7. I. Kleiner, J. Mol. Spectrosc. 260 (2010) 1.
Notes on XIAM method
 Generates cross terms of the form (JiJj + JjJi) and pαJi
in PAM basis
• We can do a van Vleck transformation to reduce
these cross terms, but we get a factored Hamiltonian
of the form
•
Rotates into RAM frame using the following angle:
Which reduces the cross term
-2FpαρJ into -2FρzpaJz which is
diagonal in this symmetric top basis
• We can then factor the Hamiltonian into four terms
HRAM = HT + Hr + Hcd + Hint :
N.B. XIAM ignores most
higher order terms associated
with the RAM Hamiltonian. For
sufficiently high barriers, you can
obtain a good effective fit of the A and E
states (as was done here)
Adapted from: I. Kleiner, J. Mol. Spectrosc. 260 (2010) 1-18.
• We can then do the proper diagonalization of this
Hamiltonian to get the appropriate torsion-rotation
energy levels, then rotate back to the PA frame to get the typical
XIAM output.