sand in the laboratory. production and interrogation of gas phase silicates. damian l kokkin and...
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Sand in the laboratory. Production and interrogation of gas phase silicates.
Damian L Kokkin and Timothy Steimle.
Silane + Oxygen and its importance
• Technological importance. SiO2 and SiO3 formed on silicon surface through oxidation process.
• Formation of silicate dust grains in the ISM.
• Second row analogue to carbon + oxygen
• Previously most experimental studies have been undertaken in rare matrices with limited gas phase studies.
– Matrix IR SiO2: Andrews 1992
– Matrix IR SiO3: Trembley et al. 1996
– PES SixOy: Lai-Sheng Wang et al. 1996
– PIE SiO, SiO2: Kostko 2009
• Theoretically challenging.– SiO3: Beste 2002 and Grein 2013. Predicted visible transitions.
– SixOy: Nayak 1998, Chu 2001
• Kinetic Studies.– Si + O containing: Gómez Martín 2009 & 2011, Hao 2014
Yang et al. Applied Physics Letters, 86, 201906, 2005
Experimental Approach
Excitation laser
Cou
nts
λem
Grating
MirrorMirror
SiH4 (2%) + N2O/O2 (<0.2%) in argon buffer gas (300psi)
Experimental Approach
Excitation laser
Cou
nts
λem
Grating
MirrorMirror
SiH4 (2%) + N2O/O2 (<0.2%) in argon buffer gas (300psi)
2D spectrum from SiH4+N2O Discharge.
Phot
on C
ount
s
ASE pumping SiH2
SiO3 Theory – Vertical Excitation Energies 1.6-2.18eV
Excitation of our unknown.
Energy (cm-1) DEnergy (cm-1)16900 -17031 13117269 36917440 54017500 600
2.09eVSpacing 2.6cm-1
→ A rotational constant of 5.2cm-1
DF of our unknown.
?
Ground State Frequency (cm-1)
271442838
Matrix IR on SiO3:287cm-1
292cm-1
855cm-1
877cm-1
1364cm-1
1340
Calculated 507cm-1
?
What else do we know.
• Lifetime: 1970±72ns
• No obvious shift or new peaks in spectrum when D2 is added to the reaction mixture.– Tried discharging SiCl4 as a precursor to remove hydrogen completely. Problems. – Lead to the first detection of SiHD.
• At pulsed dye resolution no shift in spectrum is discernable in an external magnetic field.
• Spectrum enhanced slightly with the addition of a small amount of oxygen. Too much oxygen results in only observing SiO and clogging the nozzle.
Confirmation of the SiO3 assignment as carrier of observed spectrum?
• Started trying to produce these spectral features with ablating a silicon rod in the presence of oxygen.
• Try to keep the oxygen and silane apart until the discharge to reduce the production of sand in the reaction cylinder.
• Try to measure the REMPI-TOFMS spectrum.– Problems may arise due to silicates having very high IPs.
Acknowledgements
• National Science Foundation, Division of Chemistry grant, CHE-1265885
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