K(6S)+H_2→K(4D)+H_2的碰撞能量转移

Collisional Energy Transfer for K(6S)+H_2→K(4D)+H_2

激光双光子激发K原子至6S或4D态，测量了K（6S，4D）与H2的碰撞转移截面。池温在413K，H2气压在4～40Pa范围内，K（6S，4D）-K的碰撞效应呵略去。在激发6S态的情况下，记录6S一4P时间分辨荧光信号，从荧光强度的对数描绘出的直线斜率得到6S态的有效寿命，而4D态的布居随Hz的增加而增加，因此引起4D一4P跃迁谱线的增强。在激发4D态的情况下，采用类似方法得到4D态的有效寿命，由SternVolmer方程，测得6s和4D态的辐射寿命分别为（97±15）ns和（300±45）ns。激发态K原子总的碰撞去布居截面为（1．6±0．3）×10^-14cm2（对6S态）和（40±6）×10^-16cm2（对4D态）。该总截面中包含向K原子激发态的非反应碰撞转移截面以及与H2反应生成KH的反应截面。激发6S态，测量4D→4P的时间积分荧光强度随H2气压的变化，得到6S→4D的碰撞转移截面为（1．4±0．3）×10^-14cm2。由此得到结论：K（6S）态主要是通过物理猝灭到K（4D）态，虽然在K（6S）＋H2的碰撞中，观察到了由于化学反应生成的KH的存在。

The K atoms were prepared in either the 6S or the 4D state by two-photon absorption using an OPO laser. The cross sections for deactivation of K（6S） and K（4D） by collisions with H2 were measured. The temperature of the cell body was controlled at 413 K, and H2 pressure was varied between 4 and 40 Pa. The effects of K（6S, 4D）-K collisions could be neglected in our experimental condition. On excitation of K（6S） state, the decay signal of the time-resolved fluorescence from the 6S→4P transition was monitored. The logarithmic plot for the time-resolved fluorescence of K（6S） atom was shown and the slope yielded an effective lifetime. When the pressure of H2 was successively increased, the time-resolved spectrum obviously had contri- butions from two components. At the beginning of the decay, the population of K（6S） was simply determined by the two-photon excitation and the decay curve provided the information on the effective lifetime of the K（6S） state under H2 collisions. After a prolonged period, the additional contribution of the K（6S） population from K（4D） state became important. The population of the K（4D） state increased with increasing the pressure of Hz, which leading to more intense emission of the 4D→4P transition by comparison with the case in the absence of H2. The effective lifetime for depopulation of the 4D state by collisions with H2 can be treated analogously to the 6S state. Based on the Stern-Volmer equation, radiation lifetimes are （97±15） ns for the 6S state and （300±45） ns for the 4D state. The radiation lifetimes in the absence of Hz collisions agree with those previously reported. The total cross sections for deactivation of excited K atoms by means of collisions with H2 are （1.6±0.3）×10^-14 cm2 for the 6S state and （40±6）×10^-16cm2 for the 4D state. Upon excitation to the K（6S） state, the dependence on Hz pressure of integrated fluorescence in the transition 4D→4P was measured. The cross section （1.4±0.3）×10^-14cm2 for the transition 6S→ 4D was obtained. The authors conclude that the channel for energy depletion from the 6S state is predominantly through the physical quenching to the 4D state, although the KH product has been observed in the chemical reaction.