La atom reactions with 1-pentene and 2-pentene are carried out in a laser-vaporization molecular beam source. The two reactions yield the same metal-hydrocarbon products from the dehydrogenation and carbon–carbon bond cleavage of the pentene molecules. The dehydrogenated species La(C₅H₈) is the major product, whereas the carbon–carbon bond cleaved species La(C₂H₂) and La(C₃H₄) are the minor ones. La(C₁₀H₁₈) is also observed and is presumably formed by La(C₅H₈) addition to a second pentene molecule. La(C₅H₈) and La(C₂H₂) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species from the two reactions exhibit the same transitions. Adiabatic ionization energies and metal-ligand stretching frequencies are determined for the two species, and additional methyl bending and torsional frequencies are measured for the larger one. Five possible isomers are considered for La(C₅H₈), and a C₁ metallacyclopentene (Iso A) is identified as the most possible isomer. La(C₂H₂) is confirmed to be a C_2v metallacyclopropene. The ground electronic state of each species is a doublet with a La 6s¹-based electron configuration, and ionization yields a singlet state. The formation of the lanthanacyclopentene includes La addition to the C=C double bond, La insertion into two C(sp³)—H bonds, and concerted dehydrogenation. For the 2-pentene reaction, the formation of the five-membered ring may also involve 2-pentene to 1-pentene isomerization. In addition to the metal addition and insertion, the formation of the three-membered metallacycle from 1-pentene includes C(sp³)—C(sp³) bond breakage and hydrogen migration from La to C(sp³), whereas its formation from 2-pentene may involve the ligand isomerization.

中文翻译：

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1-戊烯和2-戊烯的CH和CC键活化形成的镧-烃自由基的光谱学和形成

与1-戊烯和2-戊烯的La原子反应在激光汽化分子束源中进行。这两个反应通过戊烯分子的脱氢和碳-碳键裂解产生相同的金属-烃产物。脱氢物质La（C ₅ H ₈）是主要产物，而碳-碳键裂解的物质La（C ₂ H ₂）和La（C ₃ H ₄）是次要产物。还观察到La（C ₁₀ H ₁₈），推测是由La（C ₅ H ₈）加到第二个戊烯分子中形成的。La（C ₅ H ₈）和La（C ₂H ₂）通过质谱分析阈值电离（MATI）光谱学和量子化学计算来表征。来自两个反应的每种物质的MATI光谱显示出相同的跃迁。确定了两种物质的绝热电离能和金属配体的拉伸频率，并针对较大的一种测定了额外的甲基弯曲和扭转频率。对于La（C ₅ H ₈），考虑了5种可能的异构体，C ₁金属环戊烯（Iso A）被确定为最可能的异构体。证实La（C ₂ H ₂）是C _2v金属环丙烯。每个物种的基态电子态都是La 6s的双峰态基于^1-的电子构型，并且电离产生单重态。镧环戊烯的形成包括除了C = C双键之外的La，La插入两个C（sp ³）-H键以及协同的脱氢作用。对于2-戊烯反应，五元环的形成还可涉及2-戊烯至1-戊烯的异构化。除金属的添加和插入外，由1-戊烯形成的三元金属环还包括C（sp ³）-C（sp ³）键断裂和氢从La迁移至C（sp ³），而其形成过程2-戊烯中的α-戊烯可能涉及配体异构化。