1. Nuclear Quadrupole Coupling in SiH2I2 Due to the Presence of Two Iodine Nuclei
Discuss the Structural resolution of di-iodosilane using predictive methods and demonstrate how we can bypass some time expensive computational methods and get equally reliable results when using these predictive methods. This work was done by Eric Arsenault from our lab with collaboration of Dan Obenchein .
Eric A. Arsenault, Dan A. Obenchain, W. Orellana, and Stewart E. Novick

2. Diiodosilane: spoiler
Di-iodo molecules remain vastly understudied due to complex hyperfine structure evideent in the spectra, this is the first halosilane with 2 iodine substitution to be studied, the third molecule with 2 iodine substitutions, the first is diiodomethane, difluorodiiodomethane ( s.grubbs, steve cooke). Overcomming the reactivity to light and explosive nature of this molecule, it was able to be resolved fit from the Ghz region and the structural parameters will be presented in further slides.

3. Diiodomethane
Kisiel and co.workers used a scaling method to estimate the NQCC for CH2I2 using species that were previously studied (CH2Br, CH2Br2), this scaling method was employed in our study to estimate the NQCC of DI-iodomethane

4. NQC tensor predictions
diiodomethane diiodosilane
𝜒 CH 3 Br
𝜒 CH 3 I
χ CH 2 I 2
χ CH 2 Br 2 =
𝜒 SiH 3 Br
𝜒 SiH 3 I
χ SiH 2 I 2
χ SiH 2 Br 2 =
On the left is kisels method where red indicated the molecule understudy. The right shows what we could have used, the only issue is the dibromosilane has never been studied.
*Red indicates unknown

5. NQC tensor predictions for diiodosilane
Species
𝜒 𝑧𝑧 (MHz)
𝜒 𝑦𝑦 (MHz)
𝜒 xx (MHz)
Reference
CH3I
(51)
967.07
Carocci et al.1
CH2I2
(5)
(9)
993.4(10)
Kisiel et al.2
SiH3I *
622.55
Kewley et al.3
*No error reported
𝜒 SiH 3 I
𝜒 CH 3 I
χ CH 2 I 2
χ SiH 2 I 2 =
Prediction
Experimental
𝜒 𝑧𝑧 (MHz)
(20)
𝜒 𝑦𝑦 (MHz)
667.3
(10)
𝜒 𝑥𝑥 (MHz)
639.5
(20)
The ratio of iodomethane and di-iodomethane was used to scale the iodosaline to di-iodosilane and produce a prediction for NQCC. Point out that the diagnolized tensor from these species was used to acquire tensors independent of the specific molecular geometry. We can further take scaled NQC tensor along with a rotational matrix which I will soon discuss, and project onto the inertial axis
1S.Carocci, A.DiLieto, A.DeFanis, P.Minguzzi, S.Alanko, and J.Pietilä, J.Mol.Spectrosc. 191,368(1998).
2Z.Kisiel, L.Pszczólkowski, W.Caminati, and P.G.Favero, J.Chem.Phys. 105,1778(1996).
3R.Kewley, P.M.McKinney, and A.G.Robiette, J.Mol.Spectrosc. 34,390(1970)

6. Mention that rotational constants were used from this gas electron difraction study to obtain a rotational matrix, sturctural parameters were also compared to this study in further slides

7. Hybrid Prediction of the NQC Tensors of Iodine
Transformation
χhybrid = U-1 χscaled U
𝜒 𝑠𝑐𝑎𝑙𝑒𝑑 = −
𝑈= −
Rotation matrix for χGED
𝜒 ℎ𝑦𝑏𝑟𝑖𝑑 = −697.3 − −
Resulting prediction, χhybrid
Above we have the scaled tensor of I2Si following the rotational matrix from the Gas electron diffraction study, and a hybrid tensor in of the NQCC in the inertial axis.
Compare to experimental the the predicted tensor elements are all within 6.3% of the experimental values.
𝜒 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 = − (23) − (20) 0 − (20) (17) (29)
1Altabef, A. B.; Oberhammer, H. J. Mol. Struct. 2002, 641,

8. Spectroscopic parameters of diiodosilane
28SiH2I2 Predictiona
28SiH2I2
(92.2%)
29SiH2I2
(4.70%)
30SiH2I2
(3.09%)
𝐴 /MHz
8574
(20)
(18)
(48)
𝐵 /MHz
499
(5)
(7)
(14)
𝐶 /MHz
474
(34)
(6)
(8)
𝐷 𝐽 /kHz —
0.0362(10)
0.0343(9)
[0.0343]
𝐷 𝐽𝐾 /kHz
-3.96(17)
-3.86(28)
[-3.86]
𝜒 𝑎𝑎 /MHz
-697.3
(1)
(1)
(9)
𝜒 𝑏𝑏 /MHz
57.7
36.871(1)
36.890(1)
36.908(7)
𝜒 𝑐𝑐 /MHz
639.5
(1)
(2)
(11)
𝜒 𝑎𝑏 /MHz
912.1
(19)
(17)
(11)
𝜒 𝑎𝑎 𝐾 /kHz
20.1(7)
19.6(7)
[19.6]
𝐶 𝑎𝑎 /kHz
4.60(9)
4.37(9)
[4.37]
𝐶 𝑏𝑏 /kHz
0.567(31)
0.43(4)
[0.43]
𝐶 𝑐𝑐 /kHz
0.906(21)
0.845(29)
[0.845]
N lines
189
147 27
RMS /kHz
0.5
0.6
Here we have to table of experimental and predicted parameters,
Rotational constants,
Centrifugal Dist. Constants & nuclear spin rotation constants: not enough transitions were measured for the silicone 30 isotopologue so these parameters were held constant to the isotopologue most similar in mass (29).
Not enough transitions due to low natural abundance (92.2%), (4.70%), (3.09%)
Elements of the tenser are identical for each iodine, the sign however can not be exactly determined, for the iodine that has positive sign the other will eb negative.
3Chi (ab) element is presented
363 b-type r-branch transitions were measured
aPredicted from GED geometry

9. Diagonalized NQC tensors
Parameters
Scaled
Bailey Prediction
Experimental
28SiH2I2
29SiH2I2
30SiH2I2
127I𝜒zz (MHz)
(20)
(20)
(7)
127I𝜒yy (MHz)
667.3
672.7
(10)
(20)
(11)
127I𝜒xx(MHz)
639.5
579.3
(20)
(20)
(6) ηχ
0.05
0.07
(18)
(22)
(5)
θzb -
56.55
Here we have the diagnolized NQC tensor from the inertial axis to the quadrupolar axis (where the bond angle between the Si-I bond and the quadropolar z axis is 1o), the experimental NQCC for main isotopologue compared to the predicted values there is a difference of 3.7% for chi(zz) 1.6% chi(yy) and 6.0% for chi(xx)
In a previous investigation of 2-iodobutane, it has been found that subtle differences in chi(ZZ) can be attributed due to small changes in the C-I bond length upon isotopic substitution of this carbon. And the C-I bond length changes were estimated to differ by approximately 1.8mA, where the percent increase in mass from carbon12 to carbon 13 is 8%, the percent increase in mass for 29 from 28 and 30 from 29 is about 3.5% indicating that the bond length changes shoud decrease by less than 1.8mA
There are small differences in chi(zz) between the isotopologues, specifically an increase in 12Khz with 29 Si isotope substitution and 14khz with a 30Khz isotope substitution. This trend indicates that there are small changes in the electric field gradient of the iodine nucleus due to isotopic substitution.
However, estimating the change in bond length changes here is not straight-foward.
Specifically, due to the C2V symmetry of the molecule, the Si-I bond lengths must change in an identical manner.
There are many possible interactions between these atoms an estimation of the Bond length changes is difficult to make, more information on I-Si tensor is needed to help illuminate the trends here.

10. Chemical nature of Si-I bond
We can deduce the electronic structure in this bond through a townes dailey analysis of the measured NQCC
Pi character in this bond is evidence for (p-d)pi bonding
SiI4 has least pi character due to silicon atom having the highest degree of hybridization.
As more electronegative atoms are added the p character on the Si-I bond increases and percent of s character on Si-H bond increases. This causes increase on hybridization and decrease in Pi charachter
1W. Gordy and R.L. Cook, Microwave Molecular Spectra, 1984, Wiley; New York.
2J. Duncan, J. Harvie, D. McKean, S. Cradock, J. Mol. Struct. 145 (1986)

11. r0 structure versus GED study
This Work
Altabef et al.1
Si-I (Å)
2.4236(19)
2.423(1)
Si-H (Å)
1.475(21)
1.470(11)
I-Si-I (°)
111.27(13)
110.8(2)
I-Si-H (°)
105.9(19)
107.3(13)
Comparision between the structural parameters of from this work to the GED study mentioned previously. The paramaters are nearly identical, agreeing within experimental error.
Slight descrepency in the value for I-Si-I bond, with a disparity of only (.14o) this is can be attributed to the fact that this study only included isotopic substitution data for the central atom
1Altabef, A. B.; Oberhammer, H. J. Mol. Struct. 2002, 641,

12. Acknowledgements
Additionally
SUSANNA STEPHENS
ROBERT MELCHREIT