Does tetrahydrofuran ring open upon ionization and dissociation? A TPES and TPEPICO investigation.
Does tetrahydrofuran ring open upon ionization and dissociation? A TPES and TPEPICO investigation.
复制标题
DOI：
10.1021/jp906440p
复制
发表时间：
2009-09
期刊：
影响因子：
--
通讯作者：
P. Mayer;M. Guest;L. Cooper;L. G. Shpinkova;E. E. Rennie-E.;D. Holland;D. Shaw
中科院分区：
文献类型：
--
作者：
P. Mayer;M. Guest;L. Cooper;L. G. Shpinkova;E. E. Rennie-E.;D. Holland;D. Shaw
比较了四氢呋喃(THF)和不饱和呋喃分子的阈值光电子能谱。总的来说，这两个物种的轨道电离分布是相似的，尽管与呋喃不同，四氢呋喃只在(9b)(-1)X(2)B带表现出(适度)的振动细节。从TPES谱的起始处得到了9.445+/-0.010 eV的绝热电离能。利用阈值光电子光离子符合谱研究了电离四氢呋喃在9.9-10.4 eV光子能量范围内的氢原子损失。由RRKM拟合得到的击穿曲线E(0)为0.85+/-0.03 eV(82+/-3kJ摩尔(-1))(AE=10.30+/-0.04 eV)。如果用9.48 eV的G3IE将实验数据从光子能转换为离子内能，E(0)=0.81+/-0.01 eV(78+/-1kJ·mol(-1))。后者更接近形成环状离子1的G3E(0)值72kJ mol(-1)。我们还在B3-LYP/6-31+G(D)和G3理论水平上探讨了各种开环反应。远位异构体(*)CH(2)OCH(2)(+)比离解四氢呋喃高70kJ mol(-1)，这使其处于离解阈值为1的1kJ m ol(-1)范围内。远位异构体(包括单重态和三重态)产生的所有H损失产物的能量都显著高于离子1，排除了本实验中电离四氢呋喃通过开环反应解离到m/z 71的可能性。得到的离解增量(双匕首)S的值8+/-5JK(-1)摩尔(-1)也与1的形成一致。实验得出的E(0)值可以用来推导离子1的增量(F)H(O)(0)。与四氢呋喃离子(752.0+/-2kJ摩尔(-1))的增量(F)H(O)(0)值一起，从-154.9+/-0.7kJ摩尔(-1)和H原子(218.5+/-3kJ摩尔(-1)的实验IE为9.445+/-0.010 eV)导出E(0)82+/-3kJ摩尔(-1)的E(0)产生620kJ摩尔(-1)的离子1的增量(F)H(O)(0)。594+/-4kJ摩尔(-1))，与G3 Delta(F)H(O)(0)的621kJ摩尔(-1)符合得很好。文中还报道了直至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。
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.