Question

Please Help. Physical Chemistry question

3. If you do a careful job recording HCl and DCI spectra at the highest available resolu- tion, you will be able to see that each rotational line is split into a doublet (two closely spaced lines). Can you explain the origin for this splitting? Calculate the effective masses for the D"C1 and Dºci (H²Cl and H Cl) isotopes, and evaluate the expected shift of the vibrational fre- quency and change in the rotational constant. Hint: remember that chlorine atom has two naturally abundant isotopes, "Cl and”'Cl.

Answer 1

Each rotational line of HCl and DCl is split into a doublet because of isotope effect of Cl.Cl has 2 naturally abundant isotopes namely 35Cl and 37Cl. Based on these isotopes,the value of effective mass change. by this moment of inertia changes.thus the value of rotational constant changes according to the equations.In the following image, there is the final answer.

Rotational constant is given by b - B- Cont Rotational frequency of BL r² where I = moment of inertia = where r= bond length Ha effective mass 1. Bac // and Boot / As the effective mass increases, the ratati- -onal constant decreases ies Frequency ratsional) decreases. 3. Vibrational Frequency also decreases on increasing value of effective mass according to the equation TK where ka force con Tra l 2TC V nem -stant Ha effective mass Scan VPC CamScanne