In the interhalogen molecule Br-Cl which stretching mode will occur at the lower wavenumber, ³⁷Cl-⁷⁹Br or ³5Cl-⁸¹Br?
a. ³⁷Cl-⁷⁹Br
b. ³5Cl-⁸¹Br
c. cannot determine this because the Br-Cl bond is different in the two molecules
d. they will be at the same value