1.

For an HCI molecule find the rotational quantum numbers of two neighbouring levels whose energies differ by 7.86 meV. Thenuclei of the molecule are separated by distacne of 127.5p m.

Answer»

SOLUTION :The axis of rotation passes through the centre of mass of the `HCl` molecule.The distance of the TWO atoms from the centre of mass are
`d_(H)=(m_(cl))/(M_(Hcl))d, =(m_(H))/(m_(Hcl))d`
Thus `I=` moment of interita about the axis
`(4)/(2) m_(H)d_(H)^(2)+m_(cl)d_(cl)^(2)=(m_(H)M_(cl))/(m_(H)+m_(cl))d^(2)`
The energy difference between two NEIGHBOURING levels WHOSE quantum numbers are `J&J-1` is
`( ħ^(2))/(2I).2J=( Jħ^(2))/(I)= 7.86 meV`
Hence `J=3` and the levels have quantum numbers `2 & 3`.


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