Three new systems in the molecular spectrum of T h o have been rotationally analysed. They are located in the yellow region of the spectrum. Two bands at 5600 and 5615 .A are the 0-0 and 1-1 bands of a system named P-H. One band at 5613.A is another 0-0 band of a system called 0 -H . The states 0 and P both have = 0 with different symmetries. Another band at 5579A is also analysed. Its position in the term scheme of T h o is unknown.New measurements and an extended analysis of the previously investigated C-H transition have been performed.A term scheme and a table of molecular constants for all known states in T h o is given.

The microwave induced emission spectrum of gaseous HfS has been studied in the region 11 000-21 000cm-'. Six band systems, not previously observed, have been photographically recorded in grating spectrographs and rotationally analysed. Five of the transitions terminate on a common lower state, the X ' Z state. The five upper states are in energy order the A'& B'n, D'n, E'II and F'Z: states. The sixth system, located between the E X and D-X systems, is perturbed and is identified as the sulphide counterpart to the hafnium oxide system called C. Also, the three analysed lowest vibrational levels of the F'Z state are perturbed. Accurate molecular constants of the five regular states, the X, A, B, D, and E states, have been determined using the direct approach method. Only the most abundant isotopomer Hf'8DS3z is treated.

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Two band systems in the red region of ThO spectrum have been analysed. The systems are called R – H and S – Q. The H and Q states are known low lying excited states. The new found excited states R and S have Ω = 0- and 3 respectively. Small pertubations in the R state are studied. The upper and lower states of the previously analysed "5579 Å" band have been indentified and put into the term scheme.

On the band spectrum of H f O .