The effect of a nonresonant radiative field on low-energy rotationally inelastic collisions

We examine the effects of a linearly polarized nonresonant radiative field on the dynamics of rotationally inelastic Na⁺+N₂ collisions at eV collision energies. Our treatment is based on the Fraunhofer model of matter wave scattering and its recent extension to collisions in electric fields [M. Lemeshko, B. Friedrich, J. Chem. Phys. 129 (2008) 024301]. The nonresonant radiative field changes the effective shape of the target molecule by aligning it in the space-fixed frame. This markedly alters the differential and integral scattering cross-sections. As the cross-sections can be evaluated for a polarization of the radiative field collinear or perpendicular to the relative velocity vector, the model also offers predictions about steric asymmetry of the collisions.     

Molecular photodissociation dynamics: The time-dependent formulation

Summary The time-dependent formulation for nuclear dynamics in molecules induced by electronic excitation in a radiation field is reviewed. The present discussion is especially aiming at extracting physical observables for photodissociation and highlighting the connection to the nuclear dynamics of the process. The total dissociation probability, the probability associated with the formation of a given chemical product, and the probability that this product shows up in a specified quantum state is considered. The results are given as a function of the form of the light pulse, and special attention is given to situations where the duration of the light pulse is very short or very long.     

Propane activation by MC5H5 (M = Ni and Co): An experimental and theoretical work

The reactions of MC₅H⁺₅ (M = Ni and Co) with propane in gaseous phase have been studied with an ion trap mass spectrometer; the MC₅H⁺₅ ions are able to activate the propane molecule which undergoes a dehydrogenation reaction. At variance with the reactions of the bare metal ions no loss of methane is observed; the reaction mechanism has been explored by means of DFT calculations and a possible explanation is offered for the different reactivity of these ligated ions.     

Ar+和trans-/cis-C2H2Cl2解离电荷转移反应的离子速度成像研究(英文)

本文利用离子速度成像方法研究了Ar⁺和trans-/cis-C₂H₂Cl₂的解离电荷转移反应,根据产物离子影像明确了三个反应通道的解离机制.其中,脱氯碎片离子C₂H₂Cl⁺是主要产物,大多数分布在靶分子附近,表明解离过程主要是在大碰撞参数下通过能量共振的电荷转移后发生;同时,有少量的C₂H₂Cl⁺分布在质心附近,这是由C₂H₂Cl₂和Ar⁺在小碰撞参数下发生的紧密碰撞导致的.次要产物C₂HCl⁺展现出与C₂H₂Cl⁺相似的速度分布.而截面最低的产物C₂HCl₂⁺经历了大碰撞参数下的能量共振电荷转移后快速脱氢,基...     

Electron-transfer and chemical reactivity following collisions of Ar with C2H2

The reaction between Ar²⁺ and C₂H₂ has been studied, at centre-of-mass collision energies ranging from 3 to 7 eV, using a position-sensitive coincidence technique to detect the monocation pairs, which are formed. Sixteen different reaction channels generating pairs of monocations have been observed, these channels arise from double-electron-transfer, single-electron-transfer and chemical reactions forming ArC⁺. Examination of the scattering diagrams and energetic information extracted from the coincidence data indicate that double-electron-transfer is a direct process, which does not involve a collision complex, and the derived energetics point towards a concerted, not stepwise, mechanism for the two-electron-transfer. As is commonly observed, single-electron-transfer from C₂H₂ to Ar²⁺ takes place via a direct mechanism, again not involving complexation. Most of the C₂H₂⁺ products that are formed in the single-electron-transfer reactions possess significant (12–15 eV) internal energy and fragment rapidly within the electric field of the partner Ar⁺ ion. The chemical reactions appear to proceed via a direct mechanism involving the initial formation of ArCH⁺, which subsequently fragments to form ArC⁺.     

C60硫衍生物—C60S^＋的气相合成

Ｃ_（６０）硫衍生物──Ｃ_（６０）Ｓ~＋的气相合成刘子阳，郝国仑，郭兴华，刘淑莹（中国科学院长春应用化学研究所，长春，１３００２２）关键词Ｃ_（６０），ＣＳ_２，离子－分子反应自实现Ｃ（６０）的宏观量合成以来［１］，通过将Ｃ（６０）进行化学衍生进而改变?..     

A theoretical study on the photodissociation of C3O2

The photodecomposition of C₃O₂ into C₂O and CO is studied with the ab initio MO calculation. It is found that, starting from the second excited state of C₃O₂ (_u), the ground-state C₂O (triplet) is yielded through the bent dissociation. The stable structure of the excited triplet state of C₃O₂ as an intermediate is also demonstrated.     

Ca+-Pyridine络合物的光解反应

Photodissociation spectra of Ca+-pyridine complex was obtained by reflectron time of flight spectrum (RTOF). Two channels were found from difference photodissociation spectra, one was non-reactive Ca+ cation separation channel, the other one was active channel for product Ca+NH2. Product Ca+ was dominant in the whole region studied and the only product in 530-590 nm region, reactive product Ca+NH2 shared a little present in whole products. Action spectrum as a function of photolysis laser wavelength shows appearance peaks relevant to transitions of complex. Branching ratio supports the information of photodissociation too.     

Formation and Photodissociation of Transition Metal-Sulfur Binary Cluster Ions

Transition metal-sulfur binary cluster ions were produced by direct laser ablation and analyzed with the first stage time-of-flight mass spectrometer (TOF-MS). It was found that the distribution of the strong peaks of the stable cluster ions in the TOF-MS were not appreciably affected by the composition of the sample. The composition of the most stable metal-sulfur cluster ions, M_nS_m are different for various transition metals: Cu, n = 2m + I and n = 2m; Zn, m = n; Mn, m = n; Fe, m = n, m = n ?1 and m = n ? 2; Co, m = n ? 1, m = n ? 2, m = n ? 3, m = n ? 4 and m = n ? 5; Cr, m = n and m = n + 1; Ta, m = n + 1 and m = n + 2. Cluster ions can be selected by a mass gate, and photolyzed by an excimer laser. The photodissociation product ions were analyzed with the second stage TOF-MS. These product ions were mainly the more stable cluster ions as those given in the first stage TOF-MS.     

On the photodissociation of ozone in the range of 5–9 eV

The photoabsorption spectrum of ozone in the UV range (5–9 eV) is calculated from a short-time wave packet propagation using six potential energy surfaces obtained from ab initio electronic structure calculations. It is shown that the (unnamed) band around 7 eV, which is immediately adjacent to the intense Hartley band, is primarily due to excitation of three electronic states: 5 ¹A′ (3 ¹A₁), 6 ¹A′ (4 ¹A₁), and 4 ¹A″ (2 ¹B₁). Excitation of the state 8 ¹A′ (¹B₂) leads to a broad and intense band starting around 8 eV with a maximum near 9.1 eV. In full accord with the recent experimental study of Brouard et al. [M. Brouard, R. Cireasa, A.P. Clark, G.C. Groenenboom, G. Hancock, S.J. Horrocks, F. Quadrini, G.A.D. Ritchie, C. Vallance, J. Chem. Phys. 125 (2006) 133308], the excitation at 193 nm (6.42 eV) involves at least two states (5 ¹A′ and 4 ¹A″) different from the state excited in the Hartley band (3 ¹A′). The dynamics along the dissociation path is discussed in terms of one-dimensional potential curves. Several avoided crossings among the excited ¹A′ as well as the ¹A″ states point to a complicated fragmentation process. Although a quantitative analysis of branching ratios is not possible on the basis of the present calculations, we surmise, that in addition to and O(¹D) + O₂(¹Δ_g), the next higher spin-allowed channel, , also is likely to be a major product channel, in agreement with experimental observations.     

Using Ion-velocity Map Imaging Technique to Study Photodissociation of 2-Bromopentane

The photodissociation dynamics of 2-bromopentane at -234 nm has been investigated by utilizing ion-velocity map imaging technique. The mapped images of Br（2P3/2） （denoted as Br） and Br（2p1/2） （denoted as Br＊） fragments were analyzed by means of the speed and angular distributions, respectively. The speed distributions can be fitted with two Gaussian components which are correlated to the two independent reaction paths on the excited po- tential energy surfaces （PES）. The high-energy component is from the prompt dissociation along the C-Br stretching mode, while the low-energy one is related to the dissociation from the coupling of the C-Br stretching and bending modes. Relative quantum yield is measured to be 0.892 for Br in the photodissociation of 2-bromopentane at 234 nm. Combining the anisotropy parameter with the relative quantum yield of Br and Br fragments, the contributions of the excited 3Q0, 3Q1, and 1Q1 states to the products Br and Br were derived. The effect of alkyl branching on the mechanism of photodissociation was discussed by comparing the photodissociation processes of four isomers of bromopentane.     

Photoactivation of dichloro(ethylenediamine)platinum(II)

Photolysis of dimethylsulfoxide (dmso) solutions of the compound Pt(en)Cl₂, where en=ethylene-1,2-diamine, leads to solvolysis of the complex and formation of Pt(en)(dmso)Cl⁺. The reaction follows clean pseudo-first-order kinetics with parallel photolytically activated and thermally activated paths. Both paths are first-order in both Pt(en)Cl₂ and solvent. Eyring analysis of the rate constants for 25 °C≤T≤55 °C yielded a Gibbs energy of activation of 96 kJ mol⁻¹ for the thermal pathway and no measurable activation barrier for the photochemical pathway. The quantum yield for the photochemical path is 0.22, as determined using ferrioxalate actinometry.     

Photodissociation of 2-Bromobutane at ～265 nm by Ion-velocity Map Imaging Technique

The photodissociation dynamics of 2-bromobutane has been investigated at 264.77 and 264.86 nm by ion-velocity map imaging technique coupled with resonance-enhanced multi-photon ionization. The speed and angular distributions have been derived from the velocity map images of Br and Br*. The speed distributions of Br and Br* atoms in the photodis-sociation of 2-bromobutane at ～265 nm can be fitted using only one Gaussian function indicating that bromine fragments were produced via direct dissociation of C-Br bond. Thecontributions of the excited ³Q₀, ³Q₁, and ¹Q₁ states to the products (Br and Br*) were discussed. It is found that the nonadiabatic ¹Q₁←³Q₀ transition plays an important role for Br photofragment in the dissociation of 2-C₄H₉Br at ～265 nm. Relative quantum yield of 0.621 for Br(²P_3/2) at ～265 nm in the photodissociation of 2-bromobutane is derived. By comparing the photodissociation of 2-C₄H₉Br at ～265 nm and that that at ～234 nm, the anisotropy parameter β(Br) and β(Br*), and relative quantum yield ?(Br) decrease with increasing wavelength, the probability of curve crossing between ³Q₀ and ¹Q₁ decreases with increasing laser wavelength.