气相中二氯苯的双电荷离子[C6H4CI2]^2+和[C6H3CI]^2+的动能谱研究

本文利用质量分析离子动能(MIKES)和碰撞诱导解离(CID)技术, 研究了邻、间、对二氯苯分子在电子轰击质谱(EIMS)中产生的[C6H4CI2]^2+和[C6H4CI]^2+双电荷离子的单分子电荷分离(CS)反应。根据测定和CS反应的动能释放值T和由此估算的反应过渡态的电荷间距的最小值R, 推测过渡态的结构。有趣的是, 可以利用双电荷离子[C6H4CI2]^2+的分解反应区分二氯苯的位置异构体。     

气相中二氯苯的双电荷离子[C6H4CI2]^2+和[C6H3CI]^2+的动能谱研究

本文利用质量分析离子动能(MIKES)和碰撞诱导解离(CID)技术, 研究了邻、间、对二氯苯分子在电子轰击质谱(EIMS)中产生的[C6H4CI2]^2+和[C6H4CI]^2+双电荷离子的单分子电荷分离(CS)反应。根据测定和CS反应的动能释放值T和由此估算的反应过渡态的电荷间距的最小值R, 推测过渡态的结构。有趣的是, 可以利用双电荷离子[C6H4CI2]^2+的分解反应区分二氯苯的位置异构体。     

F~2, F与I~2的化学发光反应

在流动余辉实验装置上,研究了F~2,F与I~2的化学发光反应。首次在F+I~2反应体系中观察到较强的IF(B→X)发射光谱,采用简单碰撞理论对IF(B)的振动驰豫进行估算后,得到了其振动布居,发现与F~2+I~2反应体系有明显的不同,从而推测这两个反应的激发态产物IF(B)是由不同的反应通道形成的。前者由初级反应产物I~2F与F原子进一步作用产生,而后者则由激发态的I(^2p~1~/~2)与基态的F(^2p~3~/~2)碰撞复合产生。     

苯二酚异构体双电荷离子和单电荷离子的动能谱研究

本文利用质量分析离子动能谱(MIKES)、碰撞诱导解离(CID)技术和电子捕获诱导解离(ECID)技术, 研究了邻、间、对苯二酚分子在电子轰击质谱(EIMS)中产生的双电荷离子[C6H6O2]^2^+, [C6H4O]^2^+和单电荷离子[C6H6O2]^+。根据测定的电荷分离反应动能释放值T和由此计算出的两电荷间距R, 推测出过渡态的结构。有趣的是, 可利用单电荷离子[C6H6O2]^+的MIKES/CID谱区分苯二酚异构体。     

钌铁双核配合物的合成及猝灭[Ru(bpy)~3]^2^+发光过程研究

合成了含二氮芴和联吡啶等配体的一系列新型钌铁双核配合物:[(C~1~0H~6N~2)C=N-N=CR-Fc)Ru(bpy)~2]·(PF~6)~2,[(C~1~0H~6N~2)C=N--C~6H~4-N=CR-Fc)Ru(bpy)~2]·(PF~6)~2,[(C~1~0H~6N~2)C=N-C~6H~4-C~6H~4-N=CR-Fc)Ru(bpy)~2]·(PF~6)~2,并对其进行了光谱表征,通过对该类配合物的循环伏安和发光光谱研究,讨论其激发态的氧化还原性和对[Ru(bpy)~3]^2^+发光过程的猝灭作用.研究表明猝灭过程为扩散控制的双分子交换能量传递     

纳秒强激光场中苯电离产生高价离子的研究

用25 ns脉冲Nd-YAG 532 nm的激光，在1010～1011 W•cm－2的光场强度下，利用飞行时间质谱对He、 N2、Ar载气条件下苯的激光电离过程进行了研究.发现当利用氩作为载气时，除观察到C2＋、C2H2+、C3H3+、C6H6+离子外，还观察到很强的Cq＋(q=1～3)高价离子.这些离子都有很高的平动能， C2＋的最可几平动能为12.9 eV， C3＋为37.5 eV.通过改变载气种类和压力及在不同光场强度条件下的实验，可以认为这些高价离子来源于含苯团簇的库仑爆炸过程.     

F~2+2HCl→2HF+Cl~2反应机理的密度泛函理论研究

用密度泛函理论(DFT)B3LYP方法,在6-311G^*^*基组下,计算研究了反应F~2+2HCl→2HF+Cl~2的机理。求得各可能反应途径的系列过渡态,并通过振动分析和内禀反应坐标(IRC)分析加以证实。比较反应能垒(理论计算活化能)发现,标题反应若以分子与分子作用机理进行,则需克服的最大能垒为150.63kJ.mol^-^1;若以F~2分子先裂解为F原子再反应的机理进行,则需越过能垒154.82kJ.mol^-^1,求得反应F+HCl→HF+Cl的线形和三角形两种过渡态,以三角形较稳定;求得反应HCl+Cl→H+Cl~2的两种过渡态,以线形较稳定。     

3-苯基-1-丁炔-3-醇质谱碎裂中[C8H7]^+的结构及分子内质子迁移反应

报道了3-苯基-1-丁炔-3-醇的常规电子轰击质谱(EIMS)。利用碰撞诱导解离(CID)技术研究了质谱碎裂过程中产生的[C8H7]^+的气相离子结构。同时, 氘代同位素交换、亚稳(MI)和CID实验进一步证实了m/z 103离子的形成并不是分子离子的质谱碎裂中顺次失去甲基自由基和中性CO分子的直接氢迁移的协同反应, 而是在失去CO分子前后发生了二次质子迁移反应的逐步过程。在此基础上提出了一种独特的双分子质子键合复合物中间体的碎裂机理。     

气相中二氯苯的双电荷离子[C_6H_4Cl_2]~(2+)和[C_6H_3Cl]~(2+)的动能谱研究

本文利用质量分析离子动能谱(MIKES)和碰撞诱导解离(CID)技术,研究了邻、间、对二氯苯分子在电子轰击质谱(EIMS)中产生的[C_6H_4Cl_2]~(2+)和[C_6H_3Cl]~(2+)双电荷离子的单分子电荷分离(CS)反应.根据测定的CS反应的动能释放值T和由此估算的反应过渡态的电荷间距的最小值R,推测过渡态的结构.有趣的是,可以利用双电荷离子[C_6H_4Cl_2]~(2+)的分解反应区分二氯苯的位置异构体.     

单次碰撞反应的Ba+o,m,p-C_6H_4Cl_2的实验研究及统计理论解释

本文利用激光诱导荧光(LIF)和分子束技术,在单次碰撞条件下,研究了反应Ba+o,m,p-C_6H_4Cl_2.实验得到了反应产物BaCl的LIF光谱和这些反应的相对反应截面。对LIF光谱进行计算机模拟,得到了产物BaCl的振动布居。文中利用“入口”和“出口”过渡态“松”和“紧”的概念,并假设“出口”过渡态的弯曲振动转化为产物转动后,剩余能量全部转化为产物BaCl的振动能,对反应Ba+o,m,p-C_6H_4Cl_2进行了解释。     

Differences between the internal energy depositions induced by collisional activation and by electron transfer of W(CO)6(2+) ions on collision with Ar and K targets

Doubly charged tungsten hexacarbonyl W(CO)(6) (2+) ions were made to collide with Ar and K targets to give singly and doubly charged positive ions by collision-induced dissociation (CID). The resulting ions were analyzed and detected by using a spherical electrostatic analyzer. Whereas the doubly charged fragment ions resulting from collisional activation (CA) were dominant with the Ar target, singly charged fragment ions resulting from electron transfer were dominant with the K target. The internal energy deposition in collisionally activated dissociation (CAD) evaluated with the Ar target was broad and decreased with increasing internal energy. The predominant peaks observed with the K target were associated with singly charged W(CO)(2) (+) and W(CO)(3) (+) ions: these ions were not the result of CA, but arose from dissociation induced by electron transfer (DIET). The internal energy deposition resulting from the electron transfer was very narrow and centered at a particular energy, 7.8 eV below the energy level of the W(CO)(6) (2+) ion. This narrow internal energy distribution was explained in terms of electron transfer by Landau-Zener potential crossing at a separation of 5.9 x 10(-8) cm between a W(CO)(6) (2+) ion and a K atom, and the coulombic repulsion between singly charged ions in the exit channel. A large cross section of 1.1 x 10(-14) cm(2) was estimated for electron capture of the doubly charged W(CO)(6) (2+) ion from the alkali metal target, whose ionization energy is very low. The term "collision-induced dissociation," taken literally, includes all dissociation processes induced by collision, and therefore encompasses both CAD and DIET processes in the present work. Although the terms CID and CAD have been defined similarly, we would like to propose that they should not be used interchangeably, on the basis that there are differences in the observed ions and in their intensities with Ar and K targets.     

Enhancement of ion transmission at low collision energies via modifications to the interface region of a spectrometer

The transmission efficiency of precursor and product ions decreases significantly at lower collision energies in a four-sector tandem mass spectrometer. In an effort to improve the overall ion transmission in this energy regime three modifications were made in the interface region between the two stages of mass analysis. An einzel lens was inserted prior to the deceleration lens of the collision cell block to reduce the precursor ion beam diameter. The collision cel1 block was reduced in thickness while maintaining the collision path length, thus increasing the number of ions which entered and exited the gas chamber, while removing any stray electrical fields. Finally, a second active focusing element was incorporated after the collision cell block to enhance the collection efficiency of the product ions. A tandem mass spectrum of angiotensin I obtained with this interface, at a collision cell block potential of 9200 volts, exhibited classical high energy collision-induced dissociation (CID) fragmentation patterns, a precursor ion transmission of 92% and an overall CID efficiency of approximately 7.5%. These improvements have resulted in a dramatically higher overall ion transmission at high collision cell potentials as well as sufficient sensitivity in acquiring good quality CID spectra in the lower collision energy regime (i.e., 60 eV). (460-469)     

The effects of collision energy, vibrational mode, and vibrational angular momentum on energy transfer and dissociation in NO2+-rare gas collisions: an experimental and trajectory study

A combined experimental and trajectory study of vibrationally state-selected NO2+ collisions with Ne, Ar, Kr, and Xe is presented. Ne, Ar, and Kr are similar in that only dissociation to the excited singlet oxygen channel is observed; however, the appearance energies vary by approximately 4 eV between the three rare gases, and the variation is nonmonotonic in rare gas mass. Xe behaves quite differently, allowing efficient access to the ground triplet state dissociation channel. For all four rare gases there are strong effects of NO2+ vibrational excitation that extend over the entire collision energy range, implying that vibration influences the efficiency of collision to internal energy conversion. Bending excitation is more efficient than stretching; however, bending angular momentum partially counters the enhancement. Direct dynamics trajectories for NO2+ + Kr reproduce both the collision energy and vibrational state effects observed experimentally and reveal that intracomplex charge transfer is critical for the efficient energy transfer needed to drive dissociation. The strong vibrational effects can be rationalized in terms of bending, and to a lesser extent, stretching distortion enhancing transition to the Kr+ -NO2 charge state.     

Effect of internal excitation on the collision-induced dissociation and reactivity of Co 2 +

The kinetic energy dependence of collision-induced dissociation (CID) of dicobalt ion (Co ₂ ⁺ ) with He, Ar, and Xe has been investigated using guided ion-beam mass spectrometry. The change in efficiency of CID as the target gas is changed is in general agreement with previous CID studies of other systems: the cross section with Ar is 0.5 that with Xe, and no product ions are found with He. By varying the conditions under which the reactant ions are formed, the degree of internal excitation of the dicobalt ions is changed. The internal energies can be characterized by a Maxwell-Boltzmann distribution. We find that CID and reactions with O₂ and CO are very sensitive to Co ₂ ⁺ internal energy. The bond-dissociation energy derived from this work is D^o(Co ₂ ⁺ )=2.75±0.10 eV (63.4±2.3 kcal/mol). The Co ₂ ⁺ results are compared with a previous study of Fe ₂ ⁺ .     

On the statistical nature of collision and surface-induced dissociation: a theoretical investigation of aluminum clusters

The unimolecular dissociation dynamics of aluminum clusters following collision with either a rare gas atom or a surface is investigated by classical trajectory simulations with model potentials. Two conformers of Al(6) with very distinct shapes, i.e., the spherical O(h) and planar C(2)(h) clusters, are considered in this work. The initial vibrational energy and angular momentum distributions resulting from collision, as well as the energy and angular momentum resolved lifetime distributions, of excited clusters were determined for both collision-induced dissociation (CID) and surface-induced dissociation (SID) processes. The partitioning of excitation energy acquired upon collision was found to depend on the excitation mechanism (CID or SID), as well as on the cluster molecular shape, especially in the case of CID. For both types of processes, the energy and angular momentum resolved excited cluster lifetime distributions were found to decay exponentially, in agreement with statistical theories of chemical reactions, suggesting intrinsic Rice-Ramsperger-Kassel-Marcus (RRKM) behavior. Moreover, the simulated microcanonical rate constants determined from the cluster lifetime distributions are in good agreement with the predictions of the orbiting transition state model of phase space theory (OTS/PST), which further supports the statistical character of cluster CID and SID. Thus, in the CID and SID of highly fluxional systems such as aluminum clusters, the rate of intramolecular vibrational energy redistribution (IVR) is much faster than the dissociation rate, which validates one of the key assumptions, i.e., post-collision statistical behavior, underlying the models that are routinely used to determine cluster binding energies from experimental CID/SID cross sections.     

Theoretical study of the dynamics of AR collisions with C2H6 and C2F6 at hyperthermal energy

We present a classical-trajectory study of the dynamics of high-energy (5-12 eV) collisions between Ar atoms and the C2H6 and C2F6 molecules. We have constructed the potential-energy surfaces for these systems considering separately the Ar-molecule interactions (intermolecular potential) and the interactions within the molecule (intramolecular potential). The intermolecular surfaces consist of pairwise empirical potentials derived from high-accuracy ab initio calculations. The intramolecular potentials for C2H6 and C2F6 are described using specific-reaction-parameters semiempirical Hamiltonians and are calculated "on the fly", i.e., while the trajectories are evolving. Trajectory analysis shows that C2F6 absorbs more energy than C2H6 and is more susceptible to collision-induced dissociation (CID). C-C bond-breakage processes are more important than C-H or C-F bond breakage at the energies explored in this work. Analysis of the reaction mechanism for CID processes indicates that, although C-C breakage is mostly produced by side-on collisions, head-on collisions are more efficient in producing C-F or C-H dissociation. Our results suggest that high-energy collisions between closed-shell species of the natural low-Earth-orbit environment and spacecraft can contribute to the observed degradation of polymers that coat spacecraft surfaces.     

Gas-phase ion chemistry and organic chemistry-the story of a hybrid six sector mass spectrometer--the "AutoSpec 6F"

The AutoSpec 6F mass spectrometer is a large, floor standing instrument comprising a pair of commercial EBE geometry (AutoSpec) mass spectrometers coupled in series to provide an hybrid EBE-EBE configuration, (E and B being respectively electrostatic and magnetic sectors.) It was designed in close collaboration between Professor R. Flammang and VG Analytical in Manchester, UK. It was equipped with five collision cells and allowed the recording of high energy CID (collision induced dissociation), MIKES (mass analyzed ion kinetic energy spectrometry) and NRMS (neutralization re-ionization mass spectrometry) data as well as consecutive MSn analyses. The field-free regions between sectors allowed the study of unimolecular decomposition products from long-lived metastable ions. The mass spectrometer became even more versatile when an RF-only quadrupole collision cell was installed between the second and the third electric sector. This allowed the study of associative ion/molecule reactions in the low kinetic energy regime. Bimolecular chemical reactions were performed inside the quadrupole cell when a neutral reagent was introduced and the reaction products were analyzed by high energy CID in the downstream sectors. This paper tells the history and summarizes the capabilities of this versatile instrument.     

Energetics of retro-Diels–Alder fragmentation in limonene as characterized by surface-induced dissociation,and energy- and angle-resolved mass spectrometry

Ionized limonene and related isomeric compounds have been examined by collisional activation at both gaseous and solid targets. The gas-phase collision-induced dissociation (CID) experiments were performed as a function of collision energy and scattering angle and the surface-induced dissociation (SID) experiments as a function of collision energy, in order to vary systematically the internal energy deposited in the molecular ion. The virtual absence of retro-Diels–Alder (RDA) fragmentation upon conventional CID, as compared to its importance in the electron impact (EI) mass spectrum, the subject of a study by Boyd and coworkers, was confirmed. However, as the ion internal energy was increased by raising the collision energy or the scattering angle, RDA fragmentation was observed and it became a dominant mode of fragmentation for SID at collision energies in the range of 25–50 eV. The energy deposited into the colliding ion in the SID technique is compared with that deposited upon CID in the eV and keV energy ranges and upon EI. The order obtained is: SID > EI > low-energy, multiple-collision CID > high-energy, single-collision CID > low-energy, single-collision CID. The distribution of energies in SID is narrower than in the other techniques. High internal energies are accessible by increasing the scattering angle in CID; however, this is accompanied by an increase in the width of the internal energy distribution, and it is therefore not possible to channel fragmentation predominantly into RDA by this method. It is concluded that RDA fragmentation of limonene is a high-energy process and that this is the explanation for its behavior. Isomerization, occurring through 1,3-hydrogen migrations of the molecular ions of limonene, isolimonene, terpinolene and α-terpinene, was investigated and long-lived molecular ions of the first three compounds were found to maintain distinct structures.     

Applications of collision dynamics in quadrupole mass spectrometry

Some applications of collision dynamics in the field of quadrupole mass spectrometry are presented. Previous data on the collision induced dissociation of ions in triple quadrupole mass spectrometers is reviewed. A new method to calculate the internal energy distribution of activated ions directly from the increase in the cross section for dissociation with center of mass energy is presented. This method, although approximate, demonstrates explicitly the high efficiency of transfer of translational to internal energy of organic ions. It is argued that at eV center of mass energies, collisions between protein ions and neutrals such as Ar are expected to be highly inelastic. The discovery and application of collisional cooling in radio frequency quadrupoles is reviewed. Some previously unpresented data on fragment ion energies in triple quadrupole tandem mass spectrometry are shown that demonstrate directly the loss of kinetic energy of fragment ions in the cooling process. The development of the energy loss method to measure collision cross sections of protein ions in triple quadrupole instruments is reviewed along with a new discussion of the effects of inelastic collisions in these experiments and related ion mobility experiments.     

Low-energy electron attachment to SF6. II. Temperature and pressure dependences of dissociative attachment

Low-energy electron-molecule collisions, leading to dissociative attachment through metastable anionic states, are kinetically modeled within the framework of statistical unimolecular rate theory. The reaction e(-)+SF(6)-->SF(5)(-)+F is used as an illustrative example. The modeling is applied to new measurements of branching fractions for SF(5)(-) formation in the bath gas He between 360 and 670 K at 1 and 2 Torr, and between 490 and 620 K over the range of 0.3-9 Torr. The analysis of the data follows the previous kinetic modeling of the nondissociative electron attachment, e(-)+SF(6)-->SF(6)(-), from Part I of this series. Experimental results from the present work and the literature on branching fractions and total cross sections for anion formation as functions of electron energies, bath gas temperatures and pressures, as well as observation times are analyzed. The assumption of a participation of the electronic ground state of SF(6)(-) alone suffices to model the available experimental data. A value of the dissociation energy of SF(6)(-) into SF(5)(-)+F of E(0,dis)=1.61(+/-0.05) eV is determined, which may be compared to the electron affinity of SF(6), EA=1.20(+/-0.05) eV, such as derived in Part III of this series.