在样品池条件下,用脉冲激光670.8 nm线激发Li原子基态至2P态,测量了的反应碰撞能量转移截面。 池温保持在888 K,Li原子密度为1013 cm-3量级,而H2气压控制在60-300 Pa之间,测量时间分辨荧光光谱,它由两部分组成,在脉冲激光激发的瞬间(不超过10 ns),荧光迅速增强至最大值;激发结束后,荧光强度按指数衰减,由衰减曲线得到2P态原子在不同H2气压下的有效寿命。 根据Stern-Volmer方程,有效寿命与H2气压成线性关系,由该直线的斜率给出了总的猝灭截面(25.1±4.0)×10-16 cm2,而从直线的截距得到辐射寿命为(270±54)ns。 总的猝灭截面是反应与非反应碰撞截面之和,由在不同H2气压下记录的瞬态(<10 ns)荧光快速增强信号得到反应截面为(0.2±0.1)×10-16 cm2,虽只占总猝灭截面的1/125,但它在Li(2P)+H2的碰撞传能中所起的作用是不能略去的。

At a Li density of -1013 cm-3,the lithium vapor was irradiated in a five-arm stainless steel heat pipe oven containing Li and H2 with pulses of radiation from a N2-laser-pumped dye laser,populating Li(2P) state by the Li(２S→2P) resonance transition at 670.8 nm. Typical operating pressure of H2 was 60-300 Pa. The cross section for Li(2P)+H2→LiH+H reaction was measured using method of atomic fluorescence. The decay signal of the time-resolved fluorescence from the 2Ｐ→２S transition was monitored. The decay curve of the Li(2P) can be treated as a single exponential function. The effective lifetimes of the 2P state was obtained. According to the Stern-Volmer equation,a plot of reciprocal of effective lifetimes of the 2P state quenched by H2 against its densities yielded a slope that indicated the total cross section for deactivation and an intercept (at which the H2 pressure is zero)that provided the information about the radiative lifetime of the state. The total quenching (reactive+nonreactive) cross section for deactivation of the 2P state by means of collisions with H2 is (25.1±4.0)×10-16 cm2. The reactive cross section could be obtained using results of the recording of the fluorescence signals with rapid rise in transient regime (<10 ns) Li(2P→2S)at the different H2 densities. The authors fitted a two-state rate equation model to obtain the cross section σ(Li(2P)+H2→LiH+H)=(0.2±0.1)×10-16 cm2. The authors’ results imply that reactive collisions occur on average 1/125 as often as quenching collisions. The cross section for reaction is small but not negligible.