In a vibrational-rotational spectroscopy the total energy is the sum of the energies coming from the vibration and rotation (E = E + E₁). Selection rule suggests that for transition to occur Av = ±1 and Al = ±1. At room temperature, it is assumed that the lowest vibrational state is populated and the energy can only travel upwards due to lack of population of upper vibrational states thus Av = +1. What would be the energy of a line for R, P and Q-branch if a.) Al = +1, b.) Al = -1 and c.) Al = 0 respectively.

In a vibrational-rotational spectroscopy the total energy is the sum of the energies coming from the vibration and rotation (E = E + E₁). Selection rule suggests that for transition to occur Av = ±1 and Al = ±1. At room temperature, it is assumed that the lowest vibrational state is populated and the energy can only travel upwards due to lack of population of upper vibrational states thus Av = +1. What would be the energy of a line for R, P and Q-branch if a.) Al = +1, b.) Al = -1 and c.) Al = 0 respectively.