1. The problem statement, all variables and given/known data Assign J values for P and R branches of H35cl, H37cl, d35cl, and d37cl compounds. 2. Relevant equations 3. The attempt at a solution I have a fundamental IR spectra I did on and HCL/DCL compound. I'm extremely confused how to assign J values. I've been looking online and see R can be 0, 1, 2, 3, etc but P starts at 1,2,3, etc. How did they assign these values? What I do know I peaked picks so I know the wave numbers. I can tell the P branch form the R because as the wave numbers get smaller they get more spread out. I know the less intense peaks of the doublets are the H37CL or D37CL b/c it is a less common isotope and intensities are based on number of species.