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At what temperature, the population in v = 1 level of I2 would become half the population in ground energy level ? (Given : \(\dfrac{hc\bar{v}}{k}\) = 346.5 K)

  • A.773 K
  • B.500 K
  • C.227 K
  • D.300 K

Answer: B

The temperature is 500 K.

For the vibrational levels (each non-degenerate) the Boltzmann ratio is set by the energy gap hcν̄ between v = 1 and v = 0:

\[ \frac{N_{1}}{N_{0}} = e^{-hc\bar{\nu}/kT} = \frac{1}{2} \]

\[ \begin{aligned} \frac{346.5}{T} &= \ln 2 = 0.693 \\ T &= \frac{346.5}{0.693} = 500\ \text{K} \end{aligned} \]

773 K and 227 K are 500 K with 273 added or subtracted, a slip between kelvin and degrees Celsius, and 300 K is simply room temperature.

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