One of the most interesting areas of current research in molecular physics is the study of the vibrationally excitated states of medium and large molecules. In view of the considerable amount of experimental activity in this area, one needs theoretical models within which to interpret experimental data. Using Lie algebraic method, the vibrational energy levels of nickel metalloporphyrins like Ni(OEP), Ni porphyrin and Ni(TPP) are calculated for 16 vibrational modes. The algebraic Hamiltonian $H = E_{0} + \sum_{i=1}^{n} A_{i}C_{i} + \sum_{i < j} A_{ij}C_{ij} + \sum_{i < j}^{n} \lambda_{ij}M_{ij}$, where $A_{i}$, $A_{ij}$ and $\lambda_{ij}$ are the algebraic parameters which vary from molecule to molecule and $C_{i}$, $C_{ij}$ and $M_{ij}$ are algebraic operators. The vibrational energy levels are calculated using algebraic model Hamiltonian and the results are compared with the experimental values. The results obtained by this model are very accurate.

n this paper the stretching vibrational modes of CF₄ isotopes are calculated up to first overtone using the one-dimensional vibron model for the first time. The model Hamiltonian so constructed seems to describe the C–F stretching modes accurately using a relatively small set of well-defined parameters.

Using Lie algebraic techniques and simpler expressions of the matrix elements of Majorana and Casimir operators given by us, we obtain an effective Hamiltonian operator which conveniently describes stretching vibrations of biomolecules. For a copper tetramesityl porphyrin molecule, the higher excited vibrational levels are calculated by applying the $U (2)$ algebraic approach.