DENNIS J CLOUTHIER Department of Chemistry University of Kentucky Lexington KY LASER SPECTROSCOPY OF THE ELUSIVE JETCOOLED SiCF FREE RADICAL 8 1600 90 2320 92 2380 17 3545 ID: 628248
Download Presentation The PPT/PDF document "TONY C. SMITH, Ideal Vacuum Products, L..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
TONY C. SMITH,
Ideal Vacuum Products, LLC, Albuquerque, NM
DENNIS J. CLOUTHIER, Department of Chemistry, University of Kentucky, Lexington, KY
LASER SPECTROSCOPY OF THE (ELUSIVE) JET-COOLED SiCF FREE RADICAL
8
16.00
90
232.0
92
238.0
17
35.45
68
167.3
53
126.9
&
62
53
126.9
90
232.0
150.4
10.81
5
32.1
16
57
138.9Slide2
MOTIVATIONS1. The SiCX (X=H, F, Cl) free radicals have been suggested as intermediates in semiconductor growth and etching processes.2. These radicals have a Si-C double bond in the ground state but an unusual SiC triple bond in the excited state.3. The radicals are spectroscopically interesting with a substantial Renner-Teller effect in the 2P ground states.
SiC
H
1.0625(5) Å 1.6118(1) Å
Si
C
H
1.0677(4)
Å
1.69252(8)
ÅSlide3
LITERATURE1. T. C. Smith, H. Li, D. J. Clouthier, C. T. Kingston and A. J. Merer, "The Electronic Spectrum of Silicon Methylidyne (SiCH), a Molecule with a Silicon-Carbon Triple Bond in the Excited State," J. Chem. Phys., 112, 3662-3670 (2000).2. T. C. Smith, H. Li, D. A. Hostutler, D. J. Clouthier and A. J. Merer, "Orbital Angular Momentum (Renner-Teller) Effects in the 2IIi Ground State of Silicon Methylidyne (SiCH)," J. Chem. Phys., 114, 725-734 (2001).3. T. C. Smith, D. J. Clouthier and T. C. Steimle, "Hyperfine Structure and the Stark Effect in the Electronic Spectrum of the SiCH Radical with Implications for Microwave Spectroscopy and Radioastronomy," J. Chem. Phys., 115, 817-823 (2001).4. C. J. Evans and D. J. Clouthier, "Ab initio Predictions of the Spectroscopic Parameters of the Silicon Halomethylidyne (SiCX; X=F,Cl,Br) Free Radicals," J. Chem. Phys., 117, 6439-6445 (2002).5. T. C. Smith, C. J. Evans and D. J. Clouthier, "Spectroscopic Detection of the SiCCl Free Radical,"
J. Chem. Phys., 117, 6446-6449 (2002). Slide4
Excited StateElectron Configuration:(•••2b 1
nb 4)Ground StateElectron Configuration:(•••2b 2nb 3)
SiCH 850-600 nm
Ab initio SiCF 585 nm
2
+
2
1/2
2
3/2
ELECTRONIC SPECTROSCOPY OF SiCH & SiCF
π
σ
nbSlide5
PULSED DISCHARGE JET SPECTROSCOPY
Precursor + ArgonSlide6
Commercially available (CH3)3SiCF3: Yielded very weak spectra of SiCF along with overlapping bands of SiCH, SiH2, HCF, HSiF, SiCH2 etc. PRECURSORSSlide7
Reduction of CF3SiCl3 to CF3SiH3: Fewer impurities but SiCF spectra still very weak.Extensive and rather involved syntheses of CF3SiCl3 and CF3SiF3: No spectra of SiCF!! Theorize that the strong Si-F and Si-Cl bonds are not being broken in the discharge.
ALTERNATE PRECURSORSSlide8
EXPT’L vs AB INITIO SiCF BAND CONTOURS SiCF Ab Initio: T0 = 17104 cm-1Slide9
0-0 BAND EMISSION SPECTRUM665 cm-1105 cm-1
104 cm-1SiCF Ab Initio: SiC stretch = 672 cm-1ASO = -93 cm-1 Slide10
RENNER-TELLER ANALYSIS OF EMISSION SPECTRA Expt. Theorye -0.146(5) -0.161w2 260.5(9) 272w3 665.7(8) 667 ASO -103.4(5) -93Slide11
SiCF POTENTIALS FROM EXPT’L = -0.1462A2A
2aa
Out-of-Plane Orbital
Potentials
Electron Configuration: (
•••
2
b
2
nb
3)
Linear
In-Plane OrbitalSlide12
AB INITIO MOLECULAR STRUCTURESCCSD(T)/aug-cc-p(V+d)5Z1.693 Å
1.285 Å FCSiX2Πi
~SiCF
1.592 Å
1.293 Å
A
2
Σ
+
~Slide13
Si-C BOND LENGTHSSiCHaSiCFbSiCClbSiC (Å)1.612 1.5921.610Si=C (Å)1.6931.6931.692
aExperimental determinationbCCSD(T)/aug-cc-pVTZ valueSlide14
CONCLUSIONSThe elusive SiCF free radical has been identified in the gas phase.The radical is formed in small quantities from an electric discharge through CF3Si(CH3)3 and CF3SiH3 but not CF3SiF3.Ab initio calculations indicate that SiCF has a Si-C double bond in the ground state but a triple bond in the excited state.We have now spectroscopically characterized the SiCH, SiCCl and SiCF free radicals in the gas phase.