激光溅射Ni等离子体与气相CH3OH团簇的反应

The gas phase reaction of Ni plasma and methanol clusters is studied by the laser ablation-molecular beam（LAMB） method. Five species of clustered complex ions Ni+（CH3OH）n,NiO+（CH3OH）n,H+（CH3OH）n,H3O+（CH3OH）n,CH3O-（CH3OH）n（n≤25）are observed. Interestingly,the species and sizes of the product clusters vary observably when the plasma acts on the different parts of the pulsed methanol molecular beam. When the laser ablated Ni plasma acts on the head and tail of the beam,the metal methanol complex clusters Ni+（CH3OH）n and the oxidation clusters NiO+（CH3OH）n（n=1-15）together with protonated methanol clusters H +（CH3OH）n are domain. While the plasma acts on the middle of the beam,however,Ni+（CH3OH）1-2 and H+（CH3OH）n along with the mixed methanol-water clusters H3O+（CH3OH）n（n=15-25）turn to be the main resulting clusters. By comparing the intensities and the cluster sizes of NiO+（CH3OH）n with Ni+（CH3OH）n,the formation of NiO+（CH3OH）n is contributed to the intracluster demethanation reaction of Ni+（CH3OH）n and evaporation of several methanol molecules. As the H3O+（CH3OH）n is observed only when the plasma acts on the high density part of the beam,and their intensities are only 0. 5% of the protonated methanol molecule,it is concluded that the species are partially due to the recombination of H+（CH3OH）n and water,which come from the plasma-molecule reaction.     

甲醇团簇的多光子电离质谱及其从头算

用355 nm激光对脉冲分子束超声膨胀冷却的甲醇分子进行多光子电离, 飞行时间质谱仪观测到除甲醇碎片离子外的质子化甲醇团簇(CH3OH)nH+(n=1-16), 且离子的种类及相对强度与激光相对于脉冲分子束的延时无关, 取决于团簇离子内在结构的稳定性. 结合从头算密度泛函理论, 在B3LYP/6-31G(d)基组水平上优化得到了(CH3OH)n和(CH3OH)nH+(n=1-4)的稳定构型. 振动频谱分析显示, 团簇中最强的红外振动模主要来自氢键H伸缩振动的贡献. 团簇电离后发生于团簇内的质子转移反应也可能与激光电离引起的与氢键有关的振动模激发密切相关.     

氨和甲醇团簇中的质子转移反应

应用激光多光子电离质谱和分子束技术研究了氨和甲醇二元团簇,实验观测到两个系列质子化的团簇离子: (CH3OH)nH+和(CH3OH)nNH4+(1≤n≤14 ),其产生是经过二元团簇内的质子转移反应。同时也研究了氘代甲醇CH3OD和氨混合团簇,结果表明OD原子团中的D转移概率比CH3原子团中的质子转移概率大几倍。在HF/STO-3G和MP2/6-31G*　*水平上对氨和甲醇二元团簇进行了计算,结果表明与CH3相比OH中的质子转移更加容易,因为CH3中的质子转移过程要克服高度约120 kJ/mol的能垒。     

氟丙烯在高温下的热稳定性

用单脉冲激波管研究了全氟丙烯C3F6的分解。使用H2作为清扫剂。产物包括 CH4、 C2F4、 CF3H和C2F3H,作为对断键反应过程的指示。C3F6的断键反应为 C3F6  CF3+C2F3 （1） 得到其速率常数表达式为 k（C3F6  CF3+C2F3)=10(17.4±0.2)exp-(355300±8360)/(RT) s-1 温度范围为1090 K相似文献   

激光溅射Cu等离子体与气相C2H5OH团簇的反应

用激光溅射-分子束技术研究了气相中Cu的等离子体与乙醇分子团簇的反应.观察到三种团簇正离子Cu＋(C2H5OH)n、CuO＋(C2H5OH)n、H＋(C2H5OH)n和三种团簇负离子(C2H5OH)nC2H5O－、(C2H5OH)n(H2O)OH－、(C2H5OH)n(H2O)2OH－(n≤12).详细考察了在不同的载气压力下激光烧蚀等离子体作用于脉冲分子束， 以及在一定的压力下等离子体作用于分子束不同位置时，对团簇产物种类和团簇尺寸大小的影响.分析了Cu＋(C2H5OH)n、CuO＋(C2H5OH)n、H＋(C2H5OH)n、(C2H5OH)nC2H5O－、(C2H5OH)n(H2O)OH－、(C2H5OH)n(H2O)2OH－等团簇的产生机理.     

捕获含有圣杯式十六核水簇的水-甲醇二元簇合物（H2O）20（CH3OH）4

超声反应条件下,以氧化银、2,2’-二苯基二羧酸（H2bpda）及柔性配体1,3．-（4-吡啶）丙烷（bpp）为原料,在1：1的甲醇-水混合溶剂中合成了一个全新的银配合物IAg4（bpda）2-（bpp）4·14H2O·2CH3OH]n（1）,并对该配合物进行了元素分析、红外光谱分析、热重分析以及晶体结构研究．X射线单晶结构分析表明,配合物1的空洞中包裹着一种由罕见的圣杯式十六核水簇、四个悬挂水分子及四个悬挂甲醇分子通过氢键作用所构筑的具有中心对称性的水-甲醇二元簇合物（H2O）20（CH3OH）4．其中的十六核水分子簇可看作由一组对称性相关的八核水簇相互耦合而成,而每个八核水则由两个折叠状的五核水通过共边形成．有趣地是,仔细分析发现目前的十六核水簇结构上非常类似由两个并环戊二烯通过[2＋2]环加成而得到的一种复杂的有机烃,显示出水分子簇与有机分子结构上的相似性．     

Vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters

In this work, we report on the vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuum-ultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH(+) (n = 1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH)n(H2O)H(+) (n = 2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH(+), (CH3OH)2(+), (CH3OH)nH(+) (n = 1-9), and (CH3OH)n(H2O)H(+) (n = 2-9) as a function of photon energy. With an increase in the water content in the molecular beam, there is an enhancement of photoionization intensity for the methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.     

THF/H~2O二元团簇中“幻数”现象研究

利用分子束、同步辐射光源和飞行时间质谱研究了HF/H~2O二元团簇体系,观察到了一系列组成为(THF)~n·(H~2O)~mH^+(n=2～5,m=0～n-1)离子峰,其中(THF)~n(H~2O)~n~-~2H^+(n=2～5)离子峰强为“幻数”峰。运用从头算(abinitio)分子轨道法,在HF/3-21G基组水平上对(THF)~n(H~2O)~n~-~2H^+(n=2～4)团簇几何构型进行了优化,计算结果表明团簇离子(THF)~n(H~2O)~n~-~2H^+具有较大的稳定性,解释了实验中观察到的“幻数”现象。     

IR spectroscopy of hydrogen-bonded 2-fluoropyridine-methanol clusters

The electronic and infrared spectra of 2-fluoropyridine-methanol clusters were observed in a supersonic free jet. The structure of hydrogen-bonded clusters of 2-fluoropyridine with methanol was studied on the basis of the molecular orbital calculations. The IR spectra of 2-fluoropyridine-(CH3OH)n(n = 1-3) clusters were observed with a fluorescence-detected infrared depletion (FDIR) technique in the OH and CH stretching vibrational regions. The structures of the clusters are similar to those observed for 2-fluoropyridine-(H2O)n (n = 1-3) clusters. The existence of weak hydrogen bond interaction through aromatic hydrogen was observed in the IR spectra. The theoretical calculation also supports the result. The vibrational frequencies of CH bonds in CH3 group are affected by hydrogen bond formation although these bonds do not directly relate to the hydrogen bond interaction. The B3LYP/6-311 ++G(d,p) calculations reproduce well the vibrational frequency of the hydrogen-bonded OH stretching vibrations. However, the calculated frequency of CH stretching vibration could not reproduce the IR spectra because of anharmonic interaction with closely lying overtone or combination bands for nu3 and nu9 vibrations. The vibrational shift of nu2 vibration is reproduced well with molecular orbital calculations. The calculation also shows that the frequency shift of nu2 vibration is closely related to the CH bond length at the trans position against the OH bond in hydrogen-bonded methanol.     

Modified Kelvin-Thomson equation considering ion-dipole interaction: comparison with observed ion-clustering enthalpies and entropies

The classical Kelvin-Thomson (CKT) equation does not consider the interaction of condensing molecules with the ions and hence is not able to treat polar and nonpolar molecules differently. The ion-clustering enthalpy and entropy changes predicted by CKT equation for small ions are known to be significantly less negative than those observed. In this paper, we derive a modified Kelvin-Thomson (MKT) equation, which considers the effect of dipole-ion interaction, by taking into account the kinetic energy change of condensing polar ligands as they approach the ions or the extra energy needed for dipole molecules to escape from the ion cluster. The clustering enthalpies and entropies for protonated clusters (H(+)L(n), with L=H(2)O, NH(3), CH(3)OH, and C(5)H(5)N) are calculated based on MKT equation and compared with experimental data. Our calculations indicate that enthalpy values given by MKT equation are in very good agreement with experimental results for small ions (n< or =5) of all four species investigated. MKT predictions appear to be consistent with observed enthalpies for CH(3)OH at n> or =6 and for H(2)O at n=14-25, however, MKT equation cannot reproduce the observed discontinuous transition in enthalpy changes at n=6 for NH(3) and at n=7-13 for H(2)O which is probably associated with the formation of inner shell. The stepwise entropy changes for small ions are 5-15 cal mol(-1) K(-1) more negative when the effect of dipole-ion interaction is considered, which suggests that the ordered structure of the cluster ions can somewhat be accounted for by the dipole-ion interaction term.     

激光溅射Cu等离子体与气相CH3CN团簇的反应

The gas phase reaction of Cu plasma and acetonitrile clusters is studied by the laser ablation-molecular beam（LAMB） method. Four series of clustered complex ions Cu+（CH3CN）n, CH2CN+（CH3CN）n,H+（CH3CN）n and CH3CHCN+（CH3CN）n are observed. Interestingly,the species and sizes of the product clusters vary observably when the plasma acts on the different parts of the pulsed acetonitrile molecular beam. When the laser ablated Cu plasma acts on the head of the beam,the metal acetonitrile complex clusters Cu+（CH3CN）n together with protonated acetonitrile clusters H+（CH3CN）n and deprotonated acetonitrile clusters CH2CN+ （CH3CN）n are domain,while the plasma acts on the middle of the beam. However,CH2CN+（CH3CN）n and H+（CH3CN）n along with the clusters CH3CHCN+（CH3CN）n turn out to be the main resulting clusters. By comparing the intensities and the cluster sizes of CH3CHCN+（CH3CN）n with H+（CH3CN）n and CH2CN+（CH3CN）n,the formation of CH3CHCN +（CH3CN）n is contributed to the intracluster ion-molecule reaction of acetonitrile clusters.     

Infrared plus vacuum ultraviolet spectroscopy of neutral and ionic methanol monomers and clusters: new experimental results

We present new observations of the infrared (IR) spectrum of neutral methanol and neutral and protonated methanol clusters employing IR plus vacuum ultraviolet (vuv) spectroscopic techniques. The tunable IR light covers the energy ranges of 2500-4500 cm(-1) and 5000-7500 cm(-1). The CH and OH fundamental stretch modes, the OH overtone mode, and combination bands are identified in the vibrational spectrum of supersonic expansion cooled methanol (2500-7500 cm(-1)). Cluster size selected IR plus vuv nonresonant infrared ion-dip infrared spectra of neutral methanol clusters, (CH(3)OH)(n) (n=2,[ellipsis (horizontal)],8), demonstrate that the methanol dimer has free and bonded OH stretch features, while clusters larger than the dimer display only hydrogen bonded OH stretch features. CH stretch mode spectra do not change with cluster size. These results suggest that all clusters larger than the dimer have a cyclic structure with OH groups involved in hydrogen bonding. CH groups are apparently not part of this cyclic binding network. Studies of protonated methanol cluster ions (CH(3)OH)(n)H(+) n=1,[ellipsis (horizontal)],7 are performed by size selected vuv plus IR photodissociation spectroscopy in the OH and CH stretch regions. Energies of the free and hydrogen bonded OH stretches exhibit blueshifts with increasing n, and these two modes converge to approximately 3670 and 3400 cm(-1) at cluster size n=7, respectively.     

IR plus vacuum ultraviolet spectroscopy of neutral and ionic organic acid monomers and clusters: propanoic acid

The vibrational spectrum of molecular propanoic acid, cooled in a supersonic expansion, in the region of 2500 to 7500 cm(-1) is obtained employing infrared plus vacuum ultraviolet nonresonant ionization detected spectroscopy. The fundamental and first overtone of the CH and OH stretch modes of cold propanoic acid molecules can be identified in the spectrum. Propanoic acid neutral and ionic clusters are also studied employing nonresonant ion dip and photodissociation spectroscopic techniques, respectively. For the neutral dimer, a sequence of features observed at ca. 2500-2700 cm(-1) can be assigned as combination bands of low frequency modes with the COH bending overtone; these features characterize the cyclic dimer ring structure. IR spectra of the larger neutral clusters n=3, 4, 5 indicate that they also have cyclic structures in which the OH groups are engaged in the cluster hydrogen bonding network. The CH groups are not involved in this hydrogen bonding structure. Free OH features are observed for the protonated ion clusters (C(2)H(5)COOH)(n)H(+), n=1,...,5, indicating that at least one OH group of these cluster ions is not involved in the cluster hydrogen bonding network. A comparison of the results for four hydrogen bonding neutral and ionic clusters (CH(3)OH, C(2)H(5)OH, CH(3)COOH, and C(2)H(5)COOH) is presented and discussed.     

Size-restricted proton transfer within toluene-methanol cluster ions

To understand the interaction between toluene and methanol, the chemical reactivity of [(C6H5CH3)(CH3OH) n=1-7](+) cluster ions has been investigated via tandem quadrupole mass spectrometry and through calculations. Collision Induced Dissociation (CID) experiments show that the dissociated intracluster proton transfer reaction from the toluene cation to methanol clusters, forming protonated methanol clusters, only occurs for n = 2-4. For n = 5-7, CID spectra reveal that these larger clusters have to sequentially lose methanol monomers until they reach n = 4 to initiate the deprotonation of the toluene cation. Metastable decay data indicate that for n = 3 and n = 4 (CH3OH)3H(+) is the preferred fragment ion. The calculational results reveal that both the gross proton affinity of the methanol subcluster and the structure of the cluster itself play an important role in driving this proton transfer reaction. When n = 3, the cooperative effect of the methanols in the subcluster provides the most important contribution to allow the intracluster proton transfer reaction to occur with little or no energy barrier. As n >or= 4, the methanol subcluster is able to form ring structures to stabilize the cluster structures so that direct proton transfer is not a favored process. The preferred reaction product, the (CH3OH)3H(+) cluster ion, indicates that this size-restricted reaction is driven by both the proton affinity and the enhanced stability of the resulting product.     

Intracluster ion-molecule reactions of Ti+ with C2H5OH and CF3CH2OH clusters: influence of fluorine substituents on chemical reactivity

A laser ablation-molecular beam/reflectron time-of-flight mass spectrometric technique was used to investigate the ion-molecule reactions that proceed within Ti+(ROH)n (R = C2H5, CF3CH2) heterocluster ions. The mass spectra exhibit a major sequence of cluster ions with the formula Ti+(OR)m(ROH)n (m = 1, 2), which is attributed to sequential insertions of Ti+ into the O-H bond of C2H5OH or CF3CH2OH molecules within the heteroclusters, followed by H eliminations. The TiO+ and TiOH+ ions produced from the reactions of Ti+ with C2H5OH are interpreted as arising from insertion of Ti+ into the C-O bond, followed by C2H5 and C2H6 eliminations, respectively. When Ti+ reacted with CF3CH2OH, by contrast, considerable contributions from TiFOH+, TiF2+, and TiF2OH+ ions were observed in the mass spectrum of the reaction products, indicating that F and OH abstractions are the dominant product channels. Ab initio calculations of the complex of Ti+ with 2,2,2-trifluoroethanol show that the minimum energy structure is that in which Ti+ is attached to the O atom and one of the three F atoms of 2,2,2-trifluoroethanol, forming a five-membered ring. Isotope-labeling experiments additionally show that the chemical reactivity of heterocluster ions is greatly influenced by the presence of fluorine substituents and cluster size. The reaction energetics and formation mechanisms of the observed heterocluster ions are discussed.     

Dehydrogenation of methanol by vanadium oxide and hydroxide cluster cations in the gas phase

Bare vanadium oxide and hydroxide cluster cations, V(m)O(n)+ and V(m)O(n-1) (OH)+ (m = 1-4, n = 1-10), generated by electrospray ionization, were investigated with respect to their reactivity toward methanol using mass spectrometric techniques. Several reaction channels were observed, such as abstraction of a hydrogen atom, a methyl radical, or a hydroxymethyl radical, elimination of methane, and adduct formation. Moreover, dehydrogenation of methanol to generate formaldehyde was found to occur via four different pathways. Formaldehyde was released as a free molecule either upon transfer of two hydrogen atoms to the cluster or upon transfer of an oxygen atom from the cluster to the neutral alcohol concomitant with elimination of water. Further, formaldehyde was attached to V(m)O(n)+ upon loss of H2 or neutral water to produce the cation V(m)O(n)(OCH(2))+ or V(m)O(n-1) (OCH(2))+, respectively. A reactivity screening revealed that only high-valent vanadium oxide clusters are reactive with respect to H2 uptake, oxygen transfer, and elimination of H2O, whereas smaller and low-valent cluster cations are capable of dehydrogenating methanol via elimination of H2. For comparison, the reactivity of methanol with the corresponding hydroxide cluster ions, V(m)O(n-1) (OH)+, was studied also, for which dominant pathways lead to both condensation and association products, i.e., generation of the ions V(m)O(n-1) (OCH(3))+ and V(m)O(n-1) (OH)(CH(3)OH)+, respectively.     

New ionic crystals of oppositely charged cluster ions and their characterization

By reacting Keggin-type polyoxometalate cluster anions H(2)W(12)O(40)(6)(-) (metatungstate) or Co(II)W(12)O(40)(6)(-) (tungstocobaltate) with the large aluminum cluster polycation [Al(30)O(8)(OH)(56)(H(2)O)(26)](18+), Keggin ion based molecular ionic compounds [delta-Al(13)O(4)(OH)(24)(H(2)O)(12)][XW(12)O(40)](OH).nH(2)O (X = H(2) (1) and Co (2); n congruent with 20) and [W(2)Al(28)O(18)(OH)(48)(H(2)O)(24)][H(2)W(12)O(40)](2).55H(2)O (3) were obtained. The polygon-shaped cluster ions are packed alternately through intercluster hydrogen bonds as well as electrostatic interactions, leaving large pores, which result from the packing of large clusters. The clusters are arranged in square pyramidal geometries, showing face-to-face interactions between them. The isolation of metastable [delta-Al(13)O(4)(OH)(24)(H(2)O)(12)](7+) and the formation of a new transition metal substituted aluminum heteropolycation [W(2)Al(28)O(18)(OH)(48)(H(2)O)(24)](12+) in 1-3 result from the slow fragmentation and recombination of Al(30) in the presence of suitable counter cluster anions with similar shape and charge.     

Mid-infrared characterization of the NH4 +(H2O)n clusters in the neighborhood of the n=20 "magic" number

Vibrational predissociation spectra are reported for size-selected NH4+ (H2O)n clusters (n=5-22) in the 2500-3900 cm(-1) region. We concentrate on the sharp free OH stretching bands to deduce the local H-bonding configurations of water molecules on the cluster surface. As in the spectra of the protonated water clusters, the free OH bands in NH4+ (H2O)n evolve from a quartet at small sizes (n<7), to a doublet around n=9, and then to a single peak at the n=20 magic number cluster, before the doublet re-emerges at larger sizes. This spectral simplification at the magic number cluster mirrors that found earlier in the H+(H2O)n clusters. We characterize the likely structures at play for the n=19 and 20 clusters with electronic structure calculations. The most stable form of the n=20 cluster is predicted to have a surface-solvated NH4+ ion that lies considerably lower in energy than isomers with the NH4+ in the interior.     

Ion/molecule reactions in the orifice-skimmer region of an atmospheric pressure Penning ionization mass spectrometer

Atmospheric pressure Penning ionization mass spectra of methanol were measured as functions of Ar or He gas pressure in the first vacuum chamber, the position of the skimmer, and the voltage applied between the orifice and the skimmer. When the orifice and the skimmer were coaxial with a distance of 4 mm, the distribution of CH3OH2+(CH3OH)n clusters was only weakly dependent on both Ar pressure (in the range of 19-220 Pa) and orifice-skimmer voltage (in the range of 1-45 V). The ion/molecule reaction CH3OH2+ + CH3OH --> CH3+(CH3OH) + H2O was observed in the free jet expansion, especially at high orifice-skimmer voltage values. When the orifice and the skimmer were off-centered and the distance between them was increased to 18 mm, the formation of large CH3OH2+(CH3OH)n clusters, as well as their dissociation, were seen. The endothermic proton transfer reaction, CH3+(CH3OH) + CH3OH --> CH3OH2+ + CH3OCH3, occurred at high orifice-skimmer voltage. The collision-induced dissociation of cluster ions by He gas in the first vacuum chamber was much more efficient than by Ar. These results demonstrated that the mass spectra are highly dependent on skimmer position and on orifice-skimmer voltage and that ions observed by mass spectrometry do not necessarily reflect the abundance of ions produced in the atmospheric pressure ion source.     

IR+vacuum ultraviolet (118 nm) nonresonant ionization spectroscopy of methanol monomers and clusters: neutral cluster distribution and size-specific detection of the OH stretch vibrations

Small methanol clusters are formed by expanding a mixture of methanol vapor seeded in helium and are detected using vacuum UV (vuv) (118 nm) single-photon ionization/linear time-of-flight mass spectrometer (TOFMS). Protonated cluster ions, (CH3OH)(n-1)H+ (n=2-8), formed through intracluster ion-molecule reactions following ionization, essentially correlate to the neutral clusters, (CH3OH)n, in the present study using 118 nm light as the ionization source. Both experimental and Born-Haber calculational results clarify that not enough excess energy is released into protonated cluster ions to initiate further fragmentation in the time scale appropriate for linear TOFMS. Size-specific spectra for (CH3OH)n (n=4 to 8) clusters in the OH stretch fundamental region are recorded by IR+vuv (118 nm) nonresonant ion-dip spectroscopy through the detection chain of IR multiphoton predissociation and subsequent vuv single-photon ionization. The general structures and gross features of these cluster spectra are consistent with previous theoretical calculations. The lowest-energy peak contributed to each cluster spectrum is redshifted with increasing cluster size from n=4 to 8, and limits near approximately 3220 cm(-1) in the heptamer and octamer. Moreover, IR+vuv nonresonant ionization detected spectroscopy is employed to study the OH stretch first overtone of the methanol monomer. The rotational temperature of the clusters is estimated to be at least 50 K based on the simulation of the monomer rotational envelope under clustering conditions.