The infrared absorption spectrum of fluoroform (CHF ₃) has been observed in the region 400 to 5550 cm[superscript -1] with a Perkin-Elmer spectrometer and, in the higher regions, a multiple path absorption cell. The theoretical shapes of a parallel and a perpendicular band have been calculated and have been confirmed by the observed spectrum. The assignments of the fundamental frequencies by Rank, Schull and Pace have been confirmed and the apparent discrepancy in the appearance of the 507.5 cm[superscript -1] band has been explained. The anharmonicity constant x₆₆ has been calculated to be -0.08 cm[superscript -1]. All of the fundamentals except ν₂ have been remeasured to be: ν₁ 3033 cm[superscript -1] ν₃ 700.1 ν₄ 1375 ν₅ 1153 ν₆ 507.5 / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A successful method of dehumidification was designed and used to maintain the relative humidity in a specially constructed room at less than 40% and at a temperature of 20°C. A wavelength drive and control system were designed and built to improve and simplify the operation of a Perkin-Elmer infrared spectrometer and of the recording accessories. The spectrometer was then calibrated and used to examine the infrared absorption spectrum of gaseous carbon disulphide. The wave numbers of six absorption bands of gaseous CS₂ were determined. The wave number value of 1535 cm.ˉ¹ which was determined for the normal frequency √3, was found to agree with a new recently published result and all previously reported bands were observed. No evidence was found which might possibly lead to any interpretation other than that the structure of the carbon disulphide molecule is linear and symmetrical. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An automatic calibration marker and wavelength scanning drive has been installed on the Perkin-Elmer infrared spectrometer and the precision of this drive was checked under various operating conditions. The optimum reproducibility was found to be 0.03 wave-drive divisions and the reproducibility under normal operating conditions was found to be G.23 wave-drive divisions at the slowest scanning speed, which is six minutes per revolution of the wave-drive drum. The spectrum of nitrogen dioxide has been examined in the NaCl and LiF prism regions and a tentative assignment of the absorption bands has been made. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The strongest features in the absorption spectrum of CS₂ in the region 2900Å to 3500Å are identified, from temperature studies, as a π → π* ¹Δu - ¹Σ⁺g transition, where the Renner-Teller effect has split the ¹Δu state into ¹B₂ and ¹A₂ component states of a bent molecule. Analysis of some of the least severely perturbed bands of the ¹B₂ - ¹Σ⁺g transitions (3300 - 2900Å) shows that they form a parallel-polarized progression in the bending vibration, to an upper state with r(C - S) = 1.54₄Å, < SĈS = 163°, and a barrier to linearity of ~ 1400 cm⁻¹. Two hitherto unrecognized progressions of 'hot' bands, a weak vibronic ∏ - ∏ and a stronger vibronic Δ - Δ progression in the region 3300Å to 3500Å, are assigned to the ¹A₂ - ¹Σ⁺g transiton. This is a new type of transition, which does not appear in cold absorption, but whose 'hot' bands can obtain an amount of intensity (proportional to K²) through Renner-Teller mixing. / Science, Faculty of / Chemistry, Department of / Graduate

I.The luminescence spectra of a number of molecular Cr(III) complexes have been investigated using standard low-temperature spectroscopic techniques. The observed transitions have been assigned, assuming octahedral micro-symmetry, as emission from either the lowest lying doublet state, ²Eg, or the lowest lying quartet state, ⁴T₂g. An empirical classification is proposed which allows one to predict whether a given complex will show phosphorescence or fluorescence at low temperatures. In general, complexes with relatively high ligand field strengths show only phosphorescence because the ²Eg state lies far below the zeroth level of the ⁴T₂g. state. Compounds with relatively weak ligand field strengths have the ⁴T₂g state as their lowest excited state and therefore show only fluorescence. Complex ions with intermediate ligand fields may emit from both levels since the latter lie within a few hundred wavenumbers of each other. The phosphorescence spectra are sharp and show vibrational structure. A line coincident in energy in absorption and emission identifies the origin of the ²Eg ↔ ⁴A₂g transitions. As these spin-forbidden transitions are intra-configurational (in the strong field limit), the vibration structure in emission and absorption is very similar, although a true mirror image relationship is not realized. In many cases the vibrational spacings have been correlated with known infra-red data. The fluorescence emission is broad and shows no vibrational structure. The ⁴T₂g ↔ ⁴A₂g transitions are inter-configurational and the emission maximum is Stokes-shifted by a few thousand wavenumbers from the absorption maximum, as expected. II. The methods that have been used in the past to derive the electron repulsion parameters, B and C, from the spectra of octahedral Cr(III) complexes have been reinvestigated. A number of Cr(III) complexes were chosen for which the spin-forbidden transitions to the three lowest doublet states are known. The complete strong field and weak field matrices have been used to derive the parameters B and C from the known spectral data. A convenient graphical method is given which makes it a simple matter to choose the "best" values of B and C. The assumption that C=4B was discarded because it is incompatible with the nephelauxetic effect. The three parameter (Δ, B, C) crystal field theory reproduces the band positions of the d-d transitions of most Cr(III) complexes to within a few hundred wavenumbers. Because the free ion theory of Condon and Shortley involves about the same uncertainty, it is felt that the results obtained here represent the best that can be obtained from the three parameter crystal field theory. / Science, Faculty of / Chemistry, Department of / Graduate

Emission spectra of Indium have been photographed over the spectral range from 340A° (177A° in 2nd order) to 9500A° using the disruptive electrodeless and spark in helium sources. About 4000 lines of Indium have been measured and 36% of these lines are classified as belonging to the spectra of InI,InII, Inlll, InlV and InV. The analyses of Inlll and InlV have been revised and extended to include 4d¹ºns(n=5 to 12), `4d¹ºns(n=5 to 9), 4d¹ºnd (n=5 to 9) and 4d¹ºnf(n=4 to 7). Polarisation theory has been applied to 4d¹ºng(n=5 to 9) and 4d¹ºnh (n=6 to 9) series and the ionization potential deduced from this is reported to be 226191.3 cm⁻¹. The dipole polarizability of the 4d¹º core is estimated to be 3.48a₀³ . Most of the expected terms of 4d⁹ 5s5p and 4d⁹ 5s6s are established for the first time. Some of the levels of 4d⁹ 5s5d are also added as well as some levels from the higher configurations 4d⁹ 5s7s and 4d⁹ 5s6d. In triply ionised Indium the new additions are to the 4d⁹5d, 4d⁹ 6d, 4d⁸5s and 4d⁹6p configurations. Houston's theory of intermediate coupling has been successfully applied to 4d⁹ns (n=5,6 and 7) terms. Tentative values are given to several levels of 4d⁸5s5p and 4d⁹4f terms. The double limit of InlV is calculated from 4d⁹ns series as 461875 cm⁻¹ and 468989 cm⁻¹. Experimental results are compared with the theoretical calculations for some of the configurations of Inlll and InlV. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Relative transition probabilities were measured for several transitions in the visible ArII spectrum. An argon-nitrogen pulsed arc of duration 90 μsec, with electron densities of 2.3 x 10¹⁷ cm⁻³ and electron temperature of 2.6 ev, was used as a source of radiation. Measurements were performed with photographic diagnostics and a rotating-mirror shutter system. The fourteen values of relative transition probabilities obtained agreed reasonably well with previous measurements. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The arc and spark spectra of antimony have been photographed in the region from λ 400 Å to λ 9000 Å. Out of the approximately 5000 lines measured, one thousand five hundred and fifty eight lines have been classified as transitions between three hundred and seventy eight established levels in the spectra of SbI, SbII, SbIII, SbIV and SbV. The transformation theory of atomic spectra has been applied in detail to all the simple configuration encountered in the analyses. The Slater parameters and Landé interval factors have been calculated from the observed values of the energy levels of the configurations. The standard deviation between calculated and observed energy levels is generally about two or three percent of the configuration width. The theory of inter-configuration perturbation has been applied successfully to analyse the levels of the SbIV configuration,where 5p² and 5s5d mutually perturb and also the levels of SbIII where a perturbation occurs between 5s5p² and 5s²5d. It was generally observed that the Landé interval factors increase as the energies of parent configurations increase, while the Slater parameters remain rather constant. This relative change implies that the coupling scheme tends to the (jj) extreme in more highly excited ions and in members with higher principal quantum numbers in a Rydberg series. It is also observed that as the nuclear change increases, the coupling scheme tends to be more jj. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Radiative lifetimes were measured for a number of electronic states in neon I. The values of the lifetimes were obtained from a measurement of the time dependence of the intensity of light while the neon gas returned spontaneously to its ground state from a state of excitation. The excitation in the gas was produced by a pulsed electron gun. A monochromator of high resolution and light gathering power was designed and built for the purpose of isolating light from single transitions. The time resolved measurements on the light intensity were made using a photomultiplier and sampling oscilloscope. The lifetime of the 2p₁ state ( Paschen notation ) in neon was measured to be 15.2 ± 0.2 x 10⁻⁹ seconds, with a possible systematical error estimated at less than 5%. The lifetime of the 2s₂ state in neon was found to be 94.5 ± 4 x 10⁻⁹ seconds . Preliminary measurements of lifetimes were made for a number of other levels in neon. The relative values of several transition probabilities in neon were determined from relative intensity measurements. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The kinetics of the recombination of chlorine atoms has been studied in a fast flow system in the pressure range 0.2 to 2.0 mm Hg. The gas phase recombination was found to follow the reaction CI + CI + M→C1₂ + M (1) with (formula omitted). Rate constants were determined for He and C1₂ as third bodies in the reaction where k₁C1₂ = 2.45 x 10¹⁶cm⁶moles⁻²sec⁻¹ and k₁He = 0.3x l0¹⁶cm⁶moles⁻²sec ⁻¹ Concurrent with this reaction was a surface recombination which may be written C1 + wall → ½C1₂ + wall (26) having a surface recombination coefficient ɤ = 6.81 x 10⁻⁵, calculated from k₂₆ = 3.9 sec⁻¹. No low pressure change in the kinetic order could be detected under the experimental conditions used. The emission accompanying the recombination was found to be a band spectrum of a (formula omitted) transition. The emission decayed according to the relation (formula omitted) indicating that the (formula omitted) state is formed in some atom recombination process. / Science, Faculty of / Chemistry, Department of / Graduate