Question

Shown below is the vibration-rotation spectrum of Hydrogen Bromide (HBr), this shows transitions between the v = 0 and v = 1 vibrational levels of the molecule.

From the data, estimate the force constant (spring constant) for this molecule, given that the relative atomic weights for H and Br are 1 m_u and 80 m_u respectively.

Why is this vibrational transition split into 2 series of lines with a “missing” line in between them at the center? For each of the absorption lines labeled A-F, state the initial and final vibrational (v) and rotational (j) quantum numbers.

The 2 series of lines are due 2 selection rule:

Left = delta j = -1

Right = delta j = +1

The missing line (…) is due to a non-allowed transition of delta j = 0.

Since delta j = 0 is not allowed, the particular gap is created.

Peak    A         j = 2, v = 1      j = 3, v = 0

Peak    B          j = 1, v = 1      j = 2, v = 0

Peak    C          j = 0, v = 1      j = 1, v = 0

Peak    D         j = 1, v = 1      j = 0, v = 0

Peak    E         j = 2, v = 1      j = 1, v = 0

Peak    F          j = 3, v = 1      j = 2, v = 0

Sketch of the vibration-rotation spectrum of HBr 0.320 0.300 0.310 0.330 0.340 Energy (eV)

Answer 1

khu

fs data 2 -1S 0.31687 -21 2 чт (0.3)