The symmetric stretch vibration in^13C36^O_2 is Raman active and occurs at 1388.

Question

The symmetric stretch vibration in^13C36^O_2 is Raman active and occurs at 1388.15 cm^-1. Estimate the Raman shift for^12C^16O_2. A sample is known to fluoresce at excitation wavelengths below 600 nm. You have access to laser sources at 514 nm and 785 nm. Assume that both sources have the same power. What is the benefit of using the 514 nm source? What is the benefit of using the 785 nm source? In general, the C-C vibration occurs around 800 cm^-2. If you use a 1, 064 nm excitation source for a Raman experiment, calculate the wavelength of the Raman line associated with the C-C vibration in nanometers. C_2H_2, acetylene, is shown here. H -C = C-H (a) Is acetylene (C_2H_2) centrosymmetric? (b) Acetylene has several vibrational modes. One vibrational mode is shown here: Is this vibrational mode Raman active, IR active, or both? Two normal modes for benzene (C_6H_6) are shown. The first occurs at 3, 061 cm^-1 (called the C-H stretch, where the hydrogen and carbon move in opposite directions) and the second at 992cm^-1 (called the ring stretch, where the hydrogen and carbons move in the same direction). Would you expect these vibrations to be Raman active? Would you expect them to be IR active? a) For a molecule with Raman-active vibrations, will every Stokes line have a corresponding anti-Stokes line? Are there certain types of molecules that will exhibit Stokes but not anti-Stokes Raman scattering? b) In your new job as patent examiner, you have come across a patent application where a company has proposed a sensor for gaseous fuel and exhaust gases. It claims that the technique is quick and highly sensitive to H_2, N_2, and 0_2. The technique makes use of the infrared absorption of these molecules. What is wrong with the technique?

Explanation / Answer

1) 1480 cm-1

4) a)acetylene is centrosymetric molecule. b) the given modes is both ir and raman active mode.

5) at 3061 cm-1 , it is both raman and ir active mode. at 992 cm-1 , it is only raman active mode.

6) a)for a given molecule there will be stokes line for corresponding antistokes line. b) there no such type molecule which exhibit stokes but not anti-stokes raman scattering. c) on using IR method we can not determine H2, N2, O2 as all these are IR inactive molecules.

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