- #1

Lily Wright

- 9

- 0

## Homework Statement

A cell of length 10 cm, containing gaseous IBr at 300 K and 5 Pa pressure is irradiated by a continuous wave laser operating at a wavelength of 532 nm and a power of 5 W.

(i) Calculate the energy of the photons. Express your answer in units of J, cm-1 and eV. From the power rating of the laser, how many photons per second are contained in the laser beam?

(ii) If the absorption coefficient of IBr at 532 nm is σ = 400 dm

^{3}mol

^{-1}cm

^{-1}, calculate the intensity of the transmitted radiation (i.e. that which passes through the cell), I

_{trans}, using the Beer-Lambert Law

(iii) Upon irradiation, IBr undergoes photodissociation to produce Br atoms in an excited state, Br* . Give an expression for the quantum yield, Φ, of Br* in terms of the rate of production k[Br* ] and the intensity of absorbed radiation, I

_{abs}. If the quantum yield is 0.1, use the result from (ii) to calculate the rate of formation of Br*

## Homework Equations

where I

_{0}is the is the incident radiation intensity calculated in (i) C is the concentration of IBr in the cell and L the length of the cell

## The Attempt at a Solution

(i) E = hc/λ = 3.73 x 10

^{-19}J (=2.328 eV; 18777.26 cm

^{-1})

5W = 5 J s

^{-1}

5/3.73 x 10

^{-19}= 1.34 x 10

^{19}photons per second

(ii) is I

_{0}the same as the value for photons per second here? I don't know the concentration of IBr in the cell?

(iii) completely lost here, found these equations: d[Br*] dt = -kf[A*] - knr[A*] = -(kf + knr)[A*]

I

_{f}= Φ

_{f}I

_{0}(1-10-A)

where:

I

_{f}= emission intensity

Φ

_{f}= quantum yield

I

_{0}= incident light intensity

A = absorbance??