Controlled formation of state selected SiO metastables using a new pyrolysis source Original Research Article

A controlled and readily reproducible thermolysis of silane (SiH4) entrained in both an argon and helium carrier is used to form the precursor whose oxidation prepares long-lived yet readily monitored SiO b3Π metastables in high yeild. A simple yet novel pyrolysis-N2O oxidation source produces the b3Π metastables, yet no evidence is obtained for the formation of the lower-lying SiO a3Σ+ state. This result, which is in sharp contrast to observations made when an oven generated, helium or argon entrained silicon beam is oxidized with N2O, suggests either an unusual symmetry constraint and selective reaction branching to the b3Π state or the highly efficient quenching of the a3Σ+ state. This implies that a surprisingly similar quenching of the a3Σ+ state must occur in distinctly different helium or argon diluted silane based environments. An analysis of the observed SiO A1Π-X1Σ+ and b3Π-X1Σ+ emission band systems produced with the silane based source demonstrates that the SiO b3Π state is formed apparently selectively in a ratio exceeding 2200 times that of the remaining SiO excited states. The results obtained with the present pyrolysis N2O source are contrasted to the continuous chemiluminescent emissions associated with thermalized silane-ozone and silane-oxygen reaction environments.v The current means of generating SiO metastables would appear to (1) allow the creation of a long path length medium for the efficient energy transfer pumping of visible chemical laser amplifiers and oscillators and (2) form the basis of a useful method for the control and efficient monitoring of SiO surface deposition processes.