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Debanjana Adhikari posted an Question

May 09, 2020 • 04:54 am

30 points

CSIR NET
Physical Sciences

How do we find if a molecule is ramman active or infrared activ??

Q42. Which one of the following active? (a) 'H-H gases of diatomic molecules is Raman, infrared, and NMR (b) c-o (c)'H-CI (d) oo Ans. (C)

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Ruby negi

hcl is correct option..
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Dhairya sharma

In order for a vibrational mode to absorb infrared light, it must result in a periodic change in the dipole moment of the molecule. Such vibrations are said to be infrared active. In general, the greater the polarity of the bond, the stronger its IRabsorption. ... Some kinds of vibrations are infrared inactive.
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In answering a question how can i find out that if a molecule changes polarisibity or dipole moment or both?? Like here answer wise HCl should change polarisibility as well as dipole moment....how can i explain it??
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dear we difine polerizibility for dielectric or for molecule which have permanent dipole moment zero like symmetric molecule while dipole moment is for polar molecule.
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poler molecules don't have centre of symmetry
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Dhairya sharma

A symmetrical vibration, without change in the dipole moment would be Raman active, and not in IR. Like the stretching of a molecule of hydrogen. Water being non linear has no vibration active in Raman.
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Dhairya sharma

Only those molecular vibrations producing a dipole–moment change are IR active, allowed in the IR, and only those molecular vibrations producing polarization of the electron cloud are Raman active, allowed in the Raman. In the vapor–phase, molecules are free to rotate in three-dimensional (3D) space.
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