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Infrared and Raman spectroscopy use symmetry, vibrational selection rules, polarization, and frequencies to determine the molecular spectrum. For diatribal molecules, there is one symmetric stretching mode active in IR if it's heteronuclear and inactive if it's homonuclear. However, it is allowed as a polarized line in Raman. The rotational fine structure helps determine the moment of inertia and bond length. Triatomic molecules can be linear symmetric, bell symmetric, or linear asymmetric, each with different activities in IR and Raman. Linear symmetric models have a center of symmetry and follow the rule of mutual exclusion. Bell symmetric and linear asymmetric types have all three modes active in both IR and Raman. Nonlinear molecules cannot produce IR bands with P and R contours. Three molecules are given to identify the number of allowed modes in IR and Raman, coincidences between IR and Raman, and polarized Raman lines. Determination of molecular spectrum using infrared and Raman spectroscopy is mainly based on the application of symmetry, the vibrational selection rules, state of polarization of the lines and observed frequencies. For diatribal molecules, there will be one totally symmetric stretching mode which is active in IR if the molecule is heteronuclear and inactive if it is homonuclear. On the contrary, it is allowed as a polarized line in Raman effect. The observation of the rotational fine structure of these hits want to determine the moment of inertia and subsequently the bond length of the molecule. Keeping this in mind, we can actually categorize the various activities shown in IR or Raman spectroscopy for different molecules. In case of triatomic molecules, the possibilities are linear symmetric, bell symmetric and linear asymmetric. The number of distinct fundamentals predicted along with their activities can be listed in the following manner. If the molecule is linear symmetric model, it has to obey the rule of mutual exclusion as the center of symmetry is present in the molecule. If it is bell symmetric or linear asymmetric type, all the three distinct modes are active in both IR and Raman. In addition, if the molecule is nonlinear, it cannot give rise to IR bands with P and R contours. In this respect, you are given a task to identify three molecules namely Y-X-Y linear, Y-X-Y buried and Y-Y-X linear. Please identify the number of fundamental allowed modes in IR, number of modes permitted in Raman effect and number of IR and Raman coincidence and number of polarized Raman lines.
