Question

which of the following transitions between rotational energy level is not allowed​

Answer 1

Explanation:

Rotational Transition Selection Rules

The transition ∆J = 0 (i.e. J" = 0 and J' = 0), but where v0 = 0 and ∆v = +1, is forbidden and the pure vibrational transition is not observed in most cases. The rotational selection rule gives rise to an R-branch (when ∆J = +1) and a P-branch (when ∆J = -1).

Answer 2

The complete question is

Which of the following transitions between rotational energy levels is not allowed

Options:

1. J = 1 → J = 0
2. J = 0 ← J = 1
3. J = 1 ← J = 2
4. J = 1 → J = 3

The correct answer is

option (4) J = 1 ← J = 3

In transitions between rotational energy levels, the selection rule for transition is Δ J = ±1.

• Here J is the rotational quantum number.

1) For transition J = 1 → J = 0

Δ J = 1 - 0

= 1

So, it is allowed.

2) For transition, J = 0 ← J = 1

Δ J = 0 - 1

= -1.

it is allowed.

3) For transition, J = 1 ← J = 2

Δ J = 2 - 1

= 1.

So, it is allowed.

4) For transition, J = 1 → J = 3

Δ J = 3 - 1

= 2.

Thus in this transition Δ J is equal to 2.

So, it is not allowed.

Hence,

option

4) J = 1 → J = 3 is the correct answer.

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