In the vibrational-rotational spectrum of a diatomic molecule, the R-branch of the spectrum is the result of which of the following transitions?
(A)ΔJ = 0; Δu = 0 (B)ΔJ = 1; Δu = 0 (C)ΔJ = 2; Δu = 0 (D)ΔJ = 1; Δu = 1
D