1. The problem statement, all variables and given/known data The infrared spectrum of CO shows a vibrational absorption peak at 2170 cm-1 (a) What is the force constant of the CO bond? (b) At what wavenumber would the corresponding peak for 14CO occur? 2. Relevant equations k=ω2μ = (2πcv)2μ 3. The attempt at a solution So I solved part a correctly and the force constant for CO = 1900N/m For part b I assumed the force constant was the same for both isotopes so : v12(√μ12/μ14) = v14 I got v14 = 2079cm-1. However, the posted answer is 2083cm-1. I realize this isn't a very big difference, but I can't see a reason why my answer shouldn't be exact if I'm using the exact wavelength given and amus for the reduced mass (as in 12 and 14 for C, and 16 for O). So am I incorrect in assuming the force constants are the same? If the force constant is different for the isotopes, how would I go about solving this question since I would have two unknowns (k14 and v14).