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