The Measurement of the Rate Constant of V-E Energy Transfer in C₂H₄-Na System

Ethylene molecules were excited to high vibrational states through multiphoton excitation by TEA CO₂ laser, then collided with Sodium atoms. Energy transfer from vibrational states of ethylene to electronic states of sodium occured.
Measuring the fluorescence from excited electronic states of sodium and fitting these curves to a proposed kinetic model, we can get the rate constant of V→E energy transfer for C₂H₄-Na.
Sodium vapor was produced by a heat pipe and adjusted by an input system with three gas pathes. The pulse of fluorescence signal was detected by PMT and observed on the screen of oscilloscope. Typical fluorescence signal can be simply discribed by a biexponential function.
The kinetic mechanism of V-E energy transfer process is following:
\mathrmC_2 \mathrmH_4+\mathrmnh v_O \xrightarrowf \mathrmC_2 \mathrmH_4^\neq
\mathrmC_2 \mathrmH_4^\neq \xrightarrowr_d dissociation
\mathrmC_2 \mathrmH_4^\neq+\mathrmC_2 \mathrmH_4 \xrightarrowq 2 \mathrmC_2 \mathrmH_4
\mathrmC_2 \mathrmH_4^\neq+\mathrmNa \undersetk_E V\stackrelk_V E\rightleftharpoons \mathrmC_2 \mathrmH_4+\mathrmNa
\mathrmNa \xrightarrowA \mathrmNa+\mathrmh \nu
From the corresponding rate equations we can get that the intensity of fluorescence is proportional to (e ^-r₁t- e^-r₂t). There is a following relation for r₁ and r₂.
r₁+r₂=k_VEP_Na+A+r_d+(k_EV+q)P_C2H₄
Since （r₁+r₂） linearly depends on the partial pressure of Na, it is possible to get the slope k_VB by varying P_Na.
In this work the temperature was kept at 400℃ and the partial pressures of P_Nawere changed between 0.06-0.18 torr. We got the k_VE=2.2 ×10⁵torr^-1sec^-1.
This result means that the probability of V-E energy transfer per collision is about 1/50. It is rather reasonable.