Department of Chemistry, University of Ottawa, 10 Marie-Curie, Ottawa, Canada K1N 6N5.
J Phys Chem A. 2009 Oct 15;113(41):10923-32. doi: 10.1021/jp906440p.
The threshold photoelectron spectrum (TPES) of tetrahydrofuran (THF) is compared to that of the unsaturated furan molecule. In general, there is a similarity in the orbital ionization profile for the two species, though unlike furan, THF exhibits (modest) vibrational detail only in the (9b)(-1) X (2)B band. An adiabatic ionization energy of 9.445 +/- 0.010 eV has been derived from the onset of the TPES spectrum. Threshold photoelectron photoion coincidence spectroscopy was used to explore the loss of a hydrogen atom from ionized THF over the photon energy range of 9.9-10.4 eV. RRKM fitting of the resulting breakdown curves yields an E(0) of 0.85 +/- 0.03 eV (82 +/- 3 kJ mol(-1)) (AE = 10.30 +/- 0.04 eV). If the G3 IE of 9.48 eV is used to convert the experimental data from photon energy to THF ion internal energy, E(0) = 0.81 +/- 0.01 eV (78 +/- 1 kJ mol(-1)). The latter value is closer to the G3 E(0) of 72 kJ mol(-1) for the formation of the cyclic ion 1. A variety of ring-opening reactions were also probed at the B3-LYP/6-31+G(d) and G3 levels of theory. The distonic isomer (*)CH(2)CH(2)CH(2)OCH(2)(+) lies 70 kJ mol(-1) higher than ionized THF, which places it within 1 kJ mol(-1) of the threshold for the dissociation to 1. All of the probed H-loss products from the distonic isomer (which includes singlet and triplet species) lie significantly higher in energy than ion 1, eliminating the possibility that ionized THF dissociates to m/z 71 via a ring-opening reaction in the present experiment. The derived Delta(double dagger)S value for the dissociation, 8 +/- 5 J K(-1) mol(-1), is also consistent with the formation of 1. The experimentally derived E(0) values can be used to derive the Delta(f)H(o)(0) for ion 1. Together with the Delta(f)H(o)(0) values for the THF ion (752.0 +/- 2 kJ mol(-1), derived from the neutral Delta(f)H(o)(0) of -154.9 +/- 0.7 kJ mol(-1) and experimental IE of 9.445 +/- 0.010 eV) and H atom (218.5 kJ mol(-1)) our E(0) of 82 +/- 3 kJ mol(-1) yields a Delta(f)H(o)(0) for ion 1 of 620 +/- 4 kJ mol(-1) (Delta(f)H(o)(298) = 594 +/- 4 kJ mol(-1)), in good agreement with the G3 Delta(f)H(o)(0) of 621 kJ mol(-1). Appearance energies for all fragment ions up to photon energies of 34 eV are also reported and discussed in comparison with the available literature.
将四氢呋喃（THF）的阈值光电子能谱（TPES）与不饱和呋喃分子的阈值光电子能谱进行比较。一般来说，两种物质的轨道电离轮廓相似，但与呋喃不同，THF 仅在（9b）（-1）X（2）B 带中表现出（适度）振动细节。从 TPES 光谱的起始处得出了 9.445 +/- 0.010 eV 的绝热电离能。使用阈值光电子光离子符合光谱法在 9.9-10.4 eV 的光子能量范围内探索从离化 THF 中失去一个氢原子。对得到的分解曲线进行 RRKM 拟合，得到 E（0）为 0.85 +/- 0.03 eV（82 +/- 3 kJ mol（-1））（AE = 10.30 +/- 0.04 eV）。如果使用 G3IE 的 9.48 eV 将实验数据从光子能量转换为 THF 离子内部能量，则 E（0）= 0.81 +/- 0.01 eV（78 +/- 1 kJ mol（-1））。后者的值更接近 G3 形成环状离子 1 的 E（0）72 kJ mol（-1）。还在 B3-LYP/6-31+G（d）和 G3 理论水平上研究了各种开环反应。离域离子（*）CH（2）CH（2）CH（2）OCH（2）（+）比离化 THF 高 70 kJ mol（-1），这使得它离 1 的离解阈值只有 1 kJ mol（-1）以内。从离域异构体（包括单重态和三重态物种）中获得的所有探测到的 H 损失产物的能量都明显高于离子 1，这排除了在本实验中通过开环反应使离化 THF 解离为 m/z 71 的可能性。所得到的离解的 Delta（双剑号）S 值为 8 +/- 5 J K（-1）mol（-1），也与 1 的形成一致。实验得出的 E（0）值可用于推导离子 1 的 Delta（f）H（o）（0）。与 THF 离子的 Delta（f）H（o）（0）值（752.0 +/- 2 kJ mol（-1），由中性 Delta（f）H（o）（0）为-154.9 +/- 0.7 kJ mol（-1）和实验 IE 为 9.445 +/- 0.010 eV）和 H 原子（218.5 kJ mol（-1））一起，我们的 E（0）为 82 +/- 3 kJ mol（-1）得出离子 1 的 Delta（f）H（o）（0）为 620 +/- 4 kJ mol（-1）（Delta（f）H（o）（298）= 594 +/- 4 kJ mol（-1）），与 G3 Delta（f）H（o）（0）的 621 kJ mol（-1）非常吻合。还报告并讨论了直至 34 eV 光子能量的所有碎片离子的出现能，并与现有文献进行了比较。
