飞秒激光场中甲醇产物离子的角分布

利用直流切片离子成像技术结合飞行时间质谱技术,我们研究了甲醇(CH_3OH)分子在800 nm飞秒激光场中的多光子解离和库仑爆炸过程.获得了甲醇分子在光场中的飞行时间质谱和产物离子的切片影像,分析得到了不同库仑爆炸通道碎片离子的动能分布和角度分布.本文对比分析了C-O键断裂产生H_2O~+的H转移通道和产生OH~+的非H转移通道的角分布,计算了不同激光强度下两个通道的各向异性参数α_2和(cos~2θ),并根据产物离子角度分布与激光强度和离子价态的关系,揭示了甲醇分子在飞秒光场中的准直机制为动力学准直.     

Pulse width effect on the dissociation probability of CH4^＋ in the intense femtosecond laser field

The electric field strength of the intense ultrashort laser pulse can reach or exceed 108 V/cm, the intensity of the Coulomb field responsible for the stability of molecules. Exposed to such intense laser fields, mole- cules become unstable, undergoing di…     

Ionization and dissociation of CH<Subscript>2</Subscript>I<Subscript>2</Subscript> and CH<Subscript>2</Subscript>ICl in femtosecond intense field

With the development of ultrafast laser technique,the femtosecond laser electric field is comparable to themolecular field experienced by valence electrons. In thiscase, the classical quantum mechanical theory, based onperturbation theory, becomes inapplicable. Theoreticalunderstanding of the interaction of molecules with intenselaser radiation is quite difficult. The Coulomb explosionhas been extensively studied[1—10] and explained by somesemiclassical models, such as the above threshold ion…     

The evolution of molecular wave packet in superstrong laser fields

Summary In this note wc numerically simulate the wave packet evolution of H₂ ⁺ in superstrong laser fields with the multiple electronic-states model. The result is that the evolution process of H₂ ⁺ wave packet is mainly determined by the laser frequency. For the high-frequency fields H₂ ⁺ wave packet extends out of the interaction region step by step. However, the H₂ ⁺ wave packet is quickly dissociated in low-frequency fields. In addition, the molecular stabilization effect can be characterized at the intensity of 8 × 10¹⁵ W/cm² for the low-frequency field ω₁.     

Thermal damage and ablation behavior of plasma sprayed Ba2SmTaO6 coatings irradiated by high power continuous laser

Ba₂SmTaO₆ laser protection coatings of ≈200 ​μm thickness were deposited onto stainless steel surfaces by air plasma spraying, and the laser irradiation resistance of the coatings was investigated. For laser irradiation with a laser power density less than 1000 ​W/cm², the coatings kept intact. For a laser power density exceeding 1500 ​W/cm², the Ba₂SmTaO₆ coatings underwent recrystallization, grain growth occurred, and certain spray morphology features disappeared by melting. In the case of a laser power density of 2000 ​W/cm² applied for 10s, the incident laser parameter was beyond the coatings protection threshold, and the coating peeled off. The samples back surface temperature kept unchanged within the first 1s of laser irradiation, indicating that Ba₂SmTaO₆ coatings have excellent laser protection capability and can limit the rise of the substrate temperature. However, the low thermal conductivity of Ba₂SmTaO₆ leads to a detrimental laser energy concentration at the beginning of the laser irradiation period on the sample front surface, resulting in a rapid increase of the surface temperature up to the melting point.     

A multiphoton ionization study of acetone using time-of-flight mass spectrometry

The 3p Rydberg states of acetone and photodissociation of the acetone cation were studied using time-of-flight (TOF) mass spectrometry. The 3p Rydberg state spectroscopy of acetone was investigated with linearly polarized two-photon resonance enhanced multiphoton ionization (REMPI) from 320 to 337 nm. Several new transition bands were observed in the spectra. In addition to the CH₃COCH₃ ⁺ ion, CH₃CO⁺ and CH₃ ⁺ fragments were observed. The laser power dependences suggest that the CH₃COCH₃ ⁺, CH₃CO⁺ and CH₃ ⁺ ions are produced in three-, four-, and four-photon processes, respectively. Production of CH₃CO⁺ and CH₃ ⁺involves excitation of the ground state acetone cation by an additional photon and subsequent decomposition of the excited acetone ion. The average translational energies of CH₃CO⁺ and CH₃ ⁺ from dissociation in CH₃COCH₃ ⁺(X) + hv → CH₃CO⁺ + CH₃ and CH₃COCH₃ ⁺(X) + hv → CH₃ ⁺ + CH₃CO, respectively, were derived from the ion TOF peak profiles.     

Dissociation of NO2 in femtosecond intense fields

The study of molecules in strong laser fields is a challenging topic in molecular science[1―10]. With the advent of short-pulse lasers, the behavior of molecules can be explored on the time scale of vibrational mo-tions. An intense and linearly polarized…     

Ionization and dissociation of acetonitrile by intense femtosecond laser pulse

Photoionization and photodissociation of CH3CN were studied by a linear time of flight mass spectrometer coupled with 800 nm, 50 fs laser pulses at intensities of 6.3×1013-1.2×1014 W/cm2. The laser power dependences for principal ions CH3CN+, CH2CN+, CHCN+ and CCN+ were measured, which are consistent with the numbers of photons required to produce the ions via multiphoton ionization and dissociation. The results show that eight-photon non-resonant multiphoton ionization is the main photoionization mechanism of the parent ion CH3CN+, while the fragment ions were produced through the dissociation of the molecules in the super-excited states.     

Photocatalytic degradation of trace-level of MicrocystinLR by nano-film of titanium dioxide

The occurrence of toxic water bloom of cyanobacte-ria algae, widely reported in eutrophic freshwater, hasbeen a serious pollution problem in recent years[1]. Mi-crocystins (MCs), the most common cyanobacteriatoxin with a cyclic heptapeptide structure (Fig…     

Photoluminescence from Si-based SiNxOy films

B⁺, C⁺, Si⁺, and As⁺ with dose of 5 × 10¹⁶ cm⁻² were implanted into SiN_xO_y, films grown on crystalline silicon by plasma-enhanced chemical vapor deposition. The ion-implanted samples exhibit their photoluminescence with different intensities and different peak wavelengths after thermal annealing. Especially, the C⁺-implanted SiN_xO_y, films show very intense photoluminescence at green-yellow color region.     

Molecule modification and mass deposition induced by the implantation of low energy Fe+ ion beams into amino acids

Fe⁺ ion beams with the energy of 110 keV were implanted into films of L(+)-cysteine (HSCH₂CH(NH₂)COOH). One of the single crystals grown in hydrochloric acid solution with the implanted samples through slow evaporation was structurally characterized by the X-ray crystallography. The crystal is monoclinic, space group C2, with a = 1.8534(4) nm, b = 0.5234(1) nm, c = 0.7212(1) nm, β= 103.72°, V = 0.67965(3) nm³, Z = 4, F(000) = 144.0, D{clac} = 1.763 g · cm⁻³, μ(MoK _a = 1.06 mm⁻¹, T = 293(2) K. R = 0.0379, wR = 0.0835 for 660 observed reflections (I > 2σ(I)). The structural formula of the crystal compound is (CH₂CH(NH₂)NO₂)ClFe (M _r = 180.38 u). Products of heavy ion beam irradiation were purified and it was directly confirmed that the implanted Fe⁺ ions had been deposited in the novel molecules. The same doses of Fe⁺ ion beams of the same energy were implanted into films of L(+)-cysteine hydrochloride monohydrate. FTIR spectroscopy of the implanted samples proved that some of the original molecules were seriously damaged and significant modifications were induced.     

Rate constants for the reaction of ozone with <Emphasis Type="Italic">n</Emphasis>-butyl, <Emphasis Type="Italic">s</Emphasis>-butyl and <Emphasis Type="Italic">t</Emphasis>-butyl methyl sulfides

The rate constants for the ozone reactions with n-butyl methyl sulfide （n-BMS, CHaCH2CH2CH2SCH3）, sec-butyl methyl sulfide （s-BMS, CH3CH2（CH3）CHSCHa） and tert-butyl methyl sulfide （t-BMS, （CH3）3CSCH3） were measured using our smog chamber under supposedly pseudo-first-order conditions at 30002 K and 760 Torr. The experimental determined rate constants for n-butyl, s-butyl and t-butyl methyl sulfide are （1.23 ± 0.06）×10-19, （5.08 ± 0.19）×10-20 and （2.26 ± 0.14）×10-20 cm3 molecule-1· s-1, respectively. The reactivity-structure relationship of the reactions was discussed and used to illustrate the mechanism of the ozone reaction with thioethers. The results enrich the kinetics data of atmospheric chemistry.     

NMR and IR investigations of ternary inclusion complexes among β-cyclodextrin, rare earth metal ions, and naphthalenediamines

Ternary inclusion complexes β-cyclodextrin (β-CD), rare earth metal ions (YbCl₃, YCl₃), and 1,8-naphthalene- diamine/1,5-naphthalenediamine are synthesized in basic aqueous media, which are characterized via ¹H NMR and IR spectroscopy. The stoichiometric proportion of β-CD:YbCl₃:1,5-naphthalenediamine is 2:1:2, that of β-CD:YCl₃:1,8-naphthalenediamine is 2:1:1, and that of β-CD:YbCl₃:1,8-naphthalenediamine is 2:1:1. The IR spectroscopy of the ternary inclusion complexes in the range of 935–1 000 cm⁻¹ reveals the existence of the coordinate bond M—O or M—N. The possible conformations of the ternary inclusion complexes are depicted. Biography: JIANG Huiming(1972–), male, Associate professor, research direction: molecular complex chemistry, supramolecular chemistry.     

Field emission of SiCN thin films bombarded by Ar<Superscript>+</Superscript> ions

SiCN thin films were synthesized by a radio frequency chemical vapor deposition (RFCVD) system on P-type Si (1 0 0) wafers using C₂H₄, SiH₄ and N₂ as raw materials, In order to get rid of the oxygen absorbed on the surface and improve the characteristics of electron field emission, Ar⁺ ions of low energy were used to bombard the samples. The field emission characteristics of SiCN thin films before and after Ar⁺ bombardment were studied in the super vacuum environment of 10⁻⁶ Pa. It was showed that the turn-on field (defined as the point where the current-voltage curve shows a sharp increase in the current density) decreased from 38 V/μm before bombardment to 25 V/μm after bombardment. And the maximum emission current density increased from 159.2 to 267.4 μA/cm². The composition before and after Ar⁺ bombardment was compared using X-ray photoelectron spectroscopy (XPS). Our results illustrated that the field emission characteristics were improved after the bombardment of Ar⁺. Foundation item: Supported by the National Natural Science Foundation of China (19975035) Biography: Ma You-peng (1978), male, Master candidate, research direction: novel functional materials film and ion beam modification of materials.     

Theoretical characterization of single-electron iodine-bond weak interactions in CH3…I-Y（Y=BH2,H,CH3,C2H3,C2H,CN,NC）systems

Iodine-involved single-electron halogen bonds (SEXBs) weak interactions in the systems of CH3···I-Y(Y = BH2, H, CH3, CH==CH2, C≡CH, CN, NC) were investigated for the first time using B3LYP/6-311++G(d,p) and MP2/aug-cc-pVTZ computational levels (the relativistic effective core potential basis set of Lanl2dz was used on iodine atom). The interaction energies between two moieties with basis set super-position error corrections for the seven complexes are -0.57, -1.36, -3.80, -2.17, -4.49,-6.33 and -8.64 kJ mol-1 (MP2/aug-cc-pVTZ ), respectively, which shows that SEXBs interactions are all weak. Natural bond orbital theory analysis revealed that charges flow from CH3 to the I-Y moiety. The total amount of natural bond orbital charge transfer (ΔNC) from the CH3 radical to I-Y increases in the order CH3…IBH2 < CH3…IH ≈ CH3…ICH3 ≈ CH3···IC2H3 < CH3…ICCH< CH3…ICN< CH3…INC. Atoms-in-molecules theory was used to investigate the topological properties of the bond critical points in the seven SEXB structures.     

Theoretical investigation on mechanism of dissociation of furan

Conclusion  According to the calculated results for the dissociation mechanism of C₄H₄O⁺, we come to a conclusion as follows:

Formation, structure and properties of GeCn± and Ge2Cn± binary clusters

The binary cluster ions Ge₂C_n⁺/Ge₂C_n^- and GeC_n⁺ have been produced by laser ablation. The parity effect is present in the negative ions Ge₂C_n^-, though it is not very prominent. While the experiments tell that the parity effect is totally not shown in the positive ions Ge₂C_n⁺. An extensive theoretical investigation on GeCn/GeC_n⁺/GeC_n^-(n=1-10) and Ge₂Cn/Ge₂C_n⁺/Ge₂C_n^-(n=1-9) has been carried out by density functional theory at B3LPY level. The calculation shows that the low-lying states of GeC_n/GeC_n⁺/GeC_n^-(n=1-10) and Ge₂C_n/Ge₂C_n⁺/Ge₂C_n^-(n=1-9) are linear structure with germanium atoms locating at terminals respectively. The electronic distributions, ionization potential (IP_ad), elec-tron affinity (EA) and increasing bonding energy reveal that the parity effect of neutral species is much stronger than that of ions, which is attributed to the valence π-electrons. It is explained that the differences between experiments and cal-culations are due to the kinetic factor in the formation of Ge₂C_n^±.     

Frequency stabilization of Nd: YVO4 mini-laser using the third-harmonic detection

Via saturated absorption spectroscopy and the third-harmonic detection technique, the hyperfine spectra of ¹²⁷I₂ near 532 nm have been observed within the tuning range of a mini Nd︰YVO₄-KTP laser. The laser is frequency stabilized against one hyperfine structure (hfs) component of ¹²⁷I₂. The analysis of error signal shows that it is possible to realize a frequency stability of 3.0×10^-13 at 1 s average time.     

Quantum chemical and topological study on the insertion reaction of dichlorcarbene with acetaldehyde

The insertion reaction mechanisms of siglet and striglet CCI2 with CH3CHO have been studied by using the DFT, NBO, CCSD（T） and AIM method. The geometries of reactions, transition state and products were completely optimized by B3LYP/6-31G（d）. All the energy of the species was obtained at the CCSD（T）/6-31G（d,p） level. The calculated results indicated that all the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet CCl2 can not only insert the Cα--H （reaction I） but also can react with Cβ--H （reaction ll）. There are three main existing pathways and the products are P1 （CH3COHCCl2）, P2 （CH2COHCHCl2） and P4[CHCl2CHCHOH] respectively. Reaction II happens more easily according to the energy changes and the barrier in rate-controlling step. In addition, the important geometries in domain pathways have been studied by AIM theory. And also, the energy changes of H in the inserted C--H bond have been investigated.     

Optimization of operation conditions for extracting lithium ions from calcium chloride-type oil field brine

Al(OH)3 was prepared to extract lithium ions from calcium chloride-type oil field brine. The influences of four factors, namely temperature, Al3+/Li+ molar ratio, OH-/Al3+ molar ratio, and contact time between Al(OH)₃ and the brine, on the yield of lithium ions were investigated. It is found that their optimal values are 35℃, 4.5, 2.6, and 6 h, respectively. In the course of the experiment, the apparent pH value was observed. The results reveal that the apparent pH value has no remarkable influence on the yield of lithium ions. Meanwhile, the effects of the concentrations of calcium ions and magnesium ions in the brine on lithium recovery were studied. The results indicate that calcium ions have minor negative influence on the yield of lithium ions under optimal conditions, and magnesium ions slightly influence the yield of lithium ions.