C_(6)H自由基B^(2)Π-X^(2)Π的O_(0)^(0)带光谱的Λ型双重分裂和寿命展宽

Λ-type Doublets and Lifetime Broadening in the B^(2)Π-X^(2)Π Electronic Origin Band of C_(6)H

本文利用狭缝超声射流等离子体结合高灵敏腔衰荡光谱在18990 cm^(-1)附近研究了C6H碳链自由基B^(2)Π-X^(2)Π电子跃迀000带谱带的高分辨光谱.通过采用一套自研的窄线宽纳秒脉冲激光光源,首次在实验上观测到了该电子跃迁谱带的A型转动线分裂,获得了B^(2)Π态精确的A型双重分裂光谱常数p’=-1.16(9)×10^(-3)cm^(-1)和q’=-1.22(7)×10^(-4)cm^(-1),并更精确地确定了考虑A型分裂后修正的B、D、γ等光谱常数.基于谱线线形展宽,获得了B^(2)Π的能级寿命~100±20 ps,并分析了其可能的来源机理.

We present a high-resolution study on the B^(2)Π-X^(2)Π electronic origin band spectrum of the C_(6)H radical with its center at~18990 cm^(-1).The C_(6)H radicals are produced in a pulsed supersonic slit-jet discharge source and detected in direct absorption by sensitive cavity ring-down spectroscopy.By using a home-made narrow linewidth nanosecond pulsed laser source,the experimental spectrum allows to resolve the A-type doublet fine structures in high-J rotational lines.A set of improved B21I state constants,including the Atype doubling parameters of p'=-1.16(9)×10^(-3)cm^(-1),Q=-1.22(7)×10^(-4)cm^(-1),are determined from analysis of the experimental spectrum.An analysis on the spectral line profile has resulted in a significant linwidth broadening of-0.05±0.01 cm^(-1),corresponding to a B^(2)Πtatelife time of~100+20 ps.The short lifetime of the excited B^(2)Πstate is proposed due to fast internal vibronic couplings to high-lying vibronic levels of lower electronic states.