Intensity variations in molecular spectra at low temperatures

• Main Author: Tyte, David Christopher
• Published: Imperial College London 1962
• Subjects: 530
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602134

In recent years many calculations of arrays of Franck-Condon factors have been made and some of these have been checked by intensity measurements under a very limited range of conditions. This thesis describes some experiments in which the intensity of the bands of the nitrogen second positive system was measured. The system was excited by a discharge through very low temperatures low pressure, mixtures of helium and nitrogen, for a large range of helium pressures. The object of this work was to measure the intensity distribution in the system when it was excited under a known range of conditions to obtain results which could be compared with aurroral observations and to investigate whether the theoretical assumptions which form the background to the calculations of the q values are valid over this range of conditions. The electronic transition moment was calculated for a number of conditions and the reliability of the q values was assessed. It was found that while the majority of the q values were reliable at low helium pressures some became less reliable at high helium pressures, the electronic transition moment was also shown to vary with helium pressure. It was concluded that the theory is valid to a first approximation for low gas pressures only. The results were also used to try to gain an insight into the excitation processes occuring and their relative importance. Intensity measurements were made on some bands of the first negative system In recent years many calculations of arrays of Franck-Condon factors have been made and some of these have been checked by intensity measurements under a very limited range of conditions. This thesis describes some experiments in which the intensity of the bands of the nitrogen second positive system was measured. The system was excited by a discharge through very low temperatures low pressure, mixtures of helium and nitrogen, for a large range of helium pressures. The object of this work was to measure the intensity distribution in the system when it was excited under a known range of conditions to obtain results which could be compared with aurroral observations and to investigate whether the theoretical assumptions which form the background to the calculations of the q values are valid over this range of conditions. The electronic transition moment was calculated for a number of conditions and the reliability of the q values was assessed. It was found that while the majority of the q values were reliable at low helium pressures some became less reliable at high helium pressures, the electronic transition moment was also shown to vary with helium pressure. It was concluded that the theory is valid to a first approximation for low gas pressures only. The results were also used to try to gain an insight into the excitation processes occuring and their relative importance. Intensity measurements were made on some bands of the first negative system