【摘要】 脉冲激光烧蚀平面铝靶产生的热原子与气相CF4,CCl4,CH2Br2的碰撞反应中,在430～600nm之间观测到激发态C2分子的发光光谱,它们可归属为Swan带的d3Πg=a3Πu跃迁中Δv=2,1,0,-1,-2五个振动序列(v′≤6)。谱强度分析表明,C2激发态可很好的用热平衡描述,其振动温度达6000K左右。同时在Δv=0和-1的振动带间观测到振荡的谱峰,它们是转动谱线叠加的结果。激光烧蚀Al产生的等离子体在膨胀中产生的激波及其本身的动能与反应气体碰撞使其解离产生C,然后复合形成C2。C2激发态d可能是通过激发态的Al(2S)经近共振传能产生,也不排除在有足够碰撞能下优先形成C2激发态b,再通过与d态的v′=6能级交叉无辐射跃迁而进入d态。更多还原

【Abstract】 The emission spectra of C 2 Swan bands transition were observed in 430 600 nm region by Q switched laser ablation target of Al reacting with CF 4, CCl 4 and CH 2Br 2 beams. Five vibration band sequences (Δ v =2, 1, 0, -1 and -2) of d 3Π g a 3Π g were identified and the largest vibration number of excited state d is 6. Using a local thermal equilibrium model, the vibrational temperature of d state was determined to be about 6 000 K. Meanwhile, some bumps, separated by about 0 3 nm, were observed between vibrational bands of Δ v =0 and -1 sequences, which were due to accidental and periodical accumulations of rotational lines belonging to several vibrational bands. The formation mechanism of excited C 2 d 3Π g state is considered as when laser induced Al plasma expansion in the background reaction gas sample, the collisions between metal particles and gas sample molecules cause the dissociation of precursors, so atomic C is produced. Meanwhile, the shock wave induced by plasma expansion might cause molecules dissociation as well. Then C atoms combine to form C 2 in the ground state X 1Σ + g ( T e=0 cm -1 ) or first excited state a 3Π u ( T e=716 cm -1 ). The electronic energy transfer between excited state Al ( 2 S 1/2 )( T e=25 348 cm -1 ) and C 2 a 3Π u state produces the excited state d 3Π g ( T e=20 022 cm -1 ). Another mechanism that may be possible is that b 3Σ - g state of C 2 is produced first, then undergoes a radiationless transition into d 3Π g state through crossing with the d 3Π g,v′=6 level. But the vibrational population of v ′<6 levels is formed by collision relaxation.更多还原