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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photodissociation Spectroscopy and Dissociation Dynamics of TiO~+(CO_2)
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Photodissociation Spectroscopy and Dissociation Dynamics of TiO~+(CO_2)

机译：TiO〜+（CO_2）的光解离光谱和解离动力学

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摘要

TiO~+(CO_2) is produced by reaction of laser-ablated titanium atoms with CO_2 and subsequent clustering, supersonically cooled, and its electronic spectroscopy was characterized by photofragment spectroscopy, monitoring loss of CO_2. The photodissociation spectrum consists of a vibrationally resolved band in the visible, with extensive progressions in the covalent Ti—O stretch (952 cm~(-1) vibrational frequency and 5 cm~(-1) anharmonicity) and in the TiO~+—CO_2 stretch (186 cm~(-1)) and rock (45 cm~(-1)). The band origin is at 13 918 cm~(-1), assigned using titanium isotope shifts, and the spectrum extends to 17 350 cm~(-1). The excited-state lifetime decreases dramatically with increasing internal energy, from 1100 ns for the lowest energy band (v'_(Ti0) = 0) to <50 ns for v'_(Ti0) = 3. The long photodissociation lifetime substantially reduces the photodissociation quantum yield at low energy, likely due to competition with fluorescence. The fluorescence rate is calculated to be k_(fl) = 7.5 x 10~5 s~(-1), based on the measured excited-state lifetimes and relative band intensities. This corresponds to an integrated oscillator strength off = 0.0056. Electronic structure calculations help to assign the spectrum of TiO~+(CO_2) and predict allowed electronic transitions of TiO~+ in the visible, which have not been previously measured. Time-dependent density functional calculations predict that the observed transition is due to B, ~2Π X, ~2Δ in the TiO~+ chromophore and that binding to CO_2 red shifts the TiO~+ transition by 1508 cm~(-1) and lowers the Ti—O stretch frequency by 16 cm~(-1). Combining the computational and experimental results, the ~2Π state of TiO~+ is predicted to lie at T_o = 15 426 f 200 cm~(-1), with frequency w_e = 968 ± 5 cm~(-1) and anharmonicity ω_ex_e = 5 cm~(-1). The calculations also predict that there is only one low-lying ~2E state of TiO~+, contrary to conclusions derived from photoelectron spectroscopy of TiO. Prospects for astronomical observation of TiO~+ via the ~211-~2Δ transition are also discussed.
机译：通过激光烧蚀钛原子与CO_2反应并随后进行簇化，超声冷却而生成TiO〜+（CO_2），并通过光电子能谱表征其电子光谱，监测CO_2的损失。光解离光谱由可见光中的振动分解带组成，在共价Ti-O拉伸中（952 cm〜（-1）振动频率和5 cm〜（-1）非谐性）和TiO〜+ CO_2拉伸（186 cm〜（-1））和岩石（45 cm〜（-1））。谱带的起始点是13918 cm〜（-1），使用钛同位素位移进行分配，光谱范围扩展到17 350 cm〜（-1）。激发态寿命随着内部能量的增加而急剧下降，从最低能带（v'_（Ti0）= 0的1100 ns）到v'_（Ti0）= 3的<50 ns。长的光解离寿命大大降低了低能量下的光解离量子产率，可能是由于与荧光的竞争。基于测得的激发态寿命和相对谱带强度，计算出的荧光速率为k_（fl）= 7.5 x 10〜5 s〜（-1）。这对应于积分振荡器强度off = 0.0056。电子结构的计算有助于分配TiO〜+（CO_2）的光谱，并预测可见光中TiO〜+的允许电子跃迁，而以前尚未测量过。随时间变化的密度泛函计算预测，观察到的转变是由于TiO〜+发色团中的B，〜2ΠX，〜2Δ所致，并且与CO_2红的结合使TiO〜+转变转变了1508 cm〜（-1）并降低了Ti-O的拉伸频率为16 cm〜（-1）。结合计算和实验结果，预测TiO〜+的〜2Π状态位于T_o = 15426 f 200 cm〜（-1），频率w_e = 968±5 cm〜（-1），非谐性ω_ex_e= 5厘米〜（-1）计算结果还预测，TiO〜+仅处于一种低洼的〜2E状态，这与TiO的光电子能谱得出的结论相反。还讨论了通过〜211-〜2Δ跃迁对TiO〜+进行天文观测的前景。

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