||This thesis reports the vibrational studies using Resonance Raman, Fourier Transform Raman, Fourier Transform Infrared Spectroscopies, and Normal Coordinate Analysis of four types of porphyrin molecules : (1) Metallo-octaethyltetraazaporphyrins (Moetap, M=FeII, FeIII, CoII, NiII, CuII, ZnII)--some of their skeletal modes are assigned on the basis of isotope shifts in 15N and 13C labelled derivatives; the dependence of the skeletal modes on the size of metal ions is investigated; v3 (CalphaNm)sym stretching is found to be extraordinarily sensitive to oxidation states of Fe in Fe(oetap). This high sensitivity is attributable to the dpi-π* overlap between the metal dpi and the skeletal π* orbitals which weakens mainly CalphaNm bonds according to the electronic distribution diagram of the π* orbital of porphyrin; a comparison with other porphyrins is made and is found that, in terms of vibrational structure, Moetap is more like metallo-phthalocyanine (Mpc) but not metallo-octaethylporphyrin (Moep). (2) Free-base octaethyltetraazaporphyrins (H2oetap)--v3, v12, v39a, v39b, and v46a and some NH characteristic modes of H2oetap are assigned ; again, in terms of vibrational structures, H2oetap is found to be more like H2pc than H2oep. (3) Metallo-porphycenes (Mppc, M=NiII, PtII)--some peaks are assigned to vibrations of specific internal coordinates based on their isotope shifts ; like porphyrins, v(CbetaCbeta) and v(CbCb) of Mppc are found to mix together separating from the mixing of v(CalphaN) and v(CalphaCbeta). The mixing of the latter two is assumed to be described by the four local-mode pictures : pyrrole (pyr) quarter ring, pyr half ringsym, pyr half ringasym, and pyr breathing; some core size sensitive modes are also found from the comparison amongst Mppc, they are found to be mainly due to v(CbetaCbeta), v(CbCb), and v(CalphaCb); unlike Moetap, spin state is found to be the dominant factor for the position of the high frequency skeletal modes of Mppc. (4) Nickel(II)-etioporphyrin-I (Nietio-I)--some skeletal and substituent modes are assigned to the vibrations of internal coordinates on the basis of isotope shift; a comparison amongst Nietio-I and Nioep and Nitpp (Ni(II)tetraphenylporphyrin) is made which reveals the close resemblance of vibrational structures for the first two as expected. In contrast with the previous assignments of Nioep and Nitpp, v15 of Nietio-I is predicted to contain γ(CmH) component according to its sensitivity to meso-d4 substitution.