High Resolution Laser Spectroscopy of Diatomic Scandium-containing Molecules

This thesis reports the spectroscopic studies of diatomic molecules formed by scandium with non-metals using the laser-ablated metal vapor reacting with jet expansion of appropriate gas mixture. These molecules provide ideal model systems for investigating the role of d electrons in chemical bonding, as scandium atom possesses only one d-electron. Electronic spectra of ScP, ScBr and ScI have been studied using laser induced fluorescence (LIF) spectroscopy. The analysis of the spectra has revealed new information on structures of these molecules.;The spectrum of ScP molecule has been observed for the first time. LIF spectrum of ten vibronic bands with v up to 4 of the [11.9]1Sigma + -- X1Sigma+ system between 775 -- 900 nm has been recorded and analyzed, accurate molecular constants for the two 1Sigma+ states involved have been determined. The equilibrium bond length in the [11.9]1Sigma + state was found to be slightly shorter than that in the X 1Sigma+ state, suggesting a greater bond order in the excited state. Detailed analysis of the structural parameters in both states indicates that simple molecular orbital theory fails for this molecule.;LIF spectra of the C1Sigma+ -- X 1Sigma+, e3Delta -- a 3Delta, and d3phi -- a3Delta systems of ScBr, and the C1Sigma+ -- X1Sigma+ system of ScI between 775 -- 900 nm were recorded. The measured line positions were fitted using a least-squares program to obtain accurate molecular constants for the C1Sigma + and X1Sigma+ states of ScI, and C1Sigma+, X1Sigma +, e3Delta, d3phi, and a 3Delta states of ScBr. Molecular orbital energy level diagrams of the molecules have been constructed to explain the origin of the observed electronic states. A comparison of the molecular constants of the low-lying electronic states of scandium monohalides from similar electronic configurations indicates a weakening of chemical bonding between the scandium and the halogen atoms down the group.