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Relative transition probabilities of spontaneous emission in the R and P branches of the A1Π→X1Σ+ (0–0) band of BH molecule have been obtained for the first time. It was observed that measured ratios of the line strengths are in agreement with corresponding ratios of Ho¨nl–London factors. Thus, the non-adiabatic effect of perturbations is negligibly small and Ho¨nl–London formulas may be used for derivation of rovibronic population densities from measured line intensities of the (0–0)R branch of BH. The (0–0)P branch is less prospective because too much overlapping by other BH emissions cannot be avoided with the moderate resolution spectrometers usually used in plasma spectroscopy. General considerations are illustrated on the example of a low-pressure plasma of a planar microwave discharge in a H2–Ar–B2H6 (64:33:3) gas mixture (total pressure 1–2.5 mbar, power 1.2–2.4 kW). The values of the rotational temperatures obtained directly for the excited electronic-vibrational states d3Πu−, v′=2 (Td2rot(H2)) and A1Π+, v′=0 (TA0rot(BH)) and those calculated in the framework of excitation-deactivation models for the ground X1Σu+, v=0 vibronic states (TX0rot(H2) and TX0rot(BH)) have been analysed. It has been observed that TX0rot(H2) and TX0rot(BH) are in excellent agreement, while compared to these values TA0rot(BH) is noticeably higher and Td2rot(H2) is about two times lower. Thus, the simultaneous measurements of intensity distributions in the rotational structure of BH and H2 emission bands can be used as a prospective method for determination of gas temperature in non-equilibrium boron and hydrogen containing plasmas. [Copyright &y& Elsevier]

The introduction of room temperature continuous wave external-cavity quantum cascade lasers (EC-QCLs) with narrow linewidths has greatly facilitated high resolution spectroscopy over wide spectral ranges in the mid-infrared (MIR) region. Using the wide tuning range of an EC-QCL we have measured the absolute line strengths of many P-branch transitions of the stretching dyad of the ν 3 fundamental band of 28 SiH 4 between 2096 and 2178 cm −1 . Furthermore, the high spectral resolution available has enabled us to resolve and measure representative examples of the tetrahedral splittings associated with each component of the P-branch. The positions of these components are in excellent agreement with spherical top data system (STDS) predictions and theoretical transitions from the TDS spectroscopic database for spherical top molecules. These are the first measurements of these line strengths of 28 SiH 4 and are an example of the applicability of high-powered, widely tunable EC-QCLs to high resolution spectroscopy. [ABSTRACT FROM AUTHOR]