INFRARED-ABSORPTION OF SILANE, AMMONIA, ACETYLENE AND DIBORANE IN THERANGE OF THE CO2-LASER EMISSION-LINES - MEASUREMENTS AND MODELING

Absorption spectra of the gases SiH4, NH3, C2H2 and of SiH4/Ar and SiH 4/B2H6 mixtures have been measured in the spectral range of the CO2 la ser from 9.2 to 10.8 mu m In agreement with literature, silane shows t he highest absorption (absorption coefficient alpha = 3.3 x 10(-2) Pa- 1 m(-1)). The deviation of the measured absorption behaviour of silane from literature, as far as the pressure dependence is concerned, can be explained by the enhanced spectral energy density in our experiment . This is confirmed by a rate-equation model involving the basic mecha nisms of V-V and V-T energy transfer between vibrationally excited sil ane molecules. In contrast to silane, the absorption coefficient a of NH, at the 10P(20) laser line is 4.5 x 10(-4) Pa-1 m(-1) at p = 20 kPa and has its maximum of 4.5 x 10(-3) Pa-1 m(-1) at the 10R(6) laser li ne. For C2H2 and B2H6, alpha is even less (less than or equal to 2.1 x 10(-5) Pa-1 m(-1) for C2H2).