Kong Fan-Ao

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

The laser pulse width effect on the dissociation probability of CH4+ irradiated by an ultrafast laser has been investigated experimentally and theoretically. The femtosecond laser at 800 nm with an intensity of 8.0 × 1013 W/cm2 was used. The observed relative yield of the primary fragment ion CH3+ increases with increasing pulse width and tends to saturate when the pulse width is longer than 120 fs. The field-assisted dissociation (FAD) model and quasi-classical trajectory (QCT) calculation were applied to predicting the dissociation probability of CH4+. The calculated probability is corrected with the molecular orientation effect and the spatial distribution of laser intensity. The modified results show that the dissociation requires at least 23 fs and saturates with long pulse widths (⩾100 fs). The result is approximately consistent with the experimental observation.

Ultrafast internal conversion and vibrational relaxation of butylphthalocyanine and tetraphenylporphyrin in solution

ultrafast internal conversion (ic) and vibrational relaxation dynamics of electronically excited butylphthalocyanine (bupc) and tetra-phenylporphyrin (tpp) molecules in solution are theoretically studied on the basis of the perturbative density operator method and the transient linear susceptibility theory. femtosecond time-resolved profile of fluorescence depletion is simulated with a single vibrational mode. the internal conversion, the vibrational relaxation and the solvation rate constants in electronically excited states are determined. the results show that the sharp peak of fluorescence depletion reflects primarily the internal conversion process from the s-2 state to the s-1 state of bupc and tpp. ic occurs in a 200 fs time scale.

铅,硫团簇的形成,反应与光解

用激光直接溅射和中级溅射两种方法产生铅／硫二元团簇，并用串级飞行时间质谱仪研究了二元团簇的组份及光解规律，用激光直接溅射铅硫混合样品时，组成为ＰｂｎＳｎ－１和ＰｂｎＳｎ的团簇丰度最大，是二元团簇的结构骨架和稳定组份，而用激光串产品和硫样品，通过铅团与硫团簇的反应，则可得到ＰｂｎＳｍ（ｎ＝１３，ｍ＝０．９）和ＰｂｎＳＭ（ｎ＝１－７，ｍ＝０－９），这两种二元团簇的产生方法对应两种没的团簇形成机理。

The Formation and Photodissociation of Copper-Sulfur Cluster Ions

Copper suffer cluster ions were produced by laser ablation on solid samples: (1) a mixture of copper and sulfur powder, (2) cuprous sulfide compound, (3) cupric sulfide compound, respectively. Two main series of cluster ions were found: (a) [Cu(Cu2S)(n)](+) (n = 0 - 22), (b) [(Cu2S)(n)](+) (n = 1 - 18). The main photodissociation channels of the cluster ions were neutral losses of Cu2S, Cu or CuS. It is obvious that the Cu2S unit plays an important role in the formation and structure of the Cu/S cluster ions, and furthermore, the filled d(10) shell eletronic configuration of copper element might be critical to the characteristic of the cluster ions.

激光光解CHBr 3 +O 2 体系的FTIR-TRS研究

Photolysis of the CHBr3+O-2 system with the 193nm laser has been investigated by means of our UV laser photolysis time-resolved infrared spectrometer. CO(v,X-1 Sigma(+)) was observed up to v=10 and population conversion up to v = 5. The quenching constants for CO(v=1 to 10) by O-2 have also been deduced. We think that the reaction CHBr3 + O-2 -> CO(v,X-1 Sigma(+)) +other products (x=1 ro 2) plays an important role under our experimental conditions.

Ionization of Methyl Acetate in Ultra-intense Lasser Field

The tunneling ionization of methyl acetate in the laser intensity range of 4.8 x 10(13) W. cm(-2) to 1.3 x 10(14) W.cm(-2) was studied. The modified Keldvsh parameter was calculated by the ab initio method. The tunneling probability was calculated by the WKB method. When the laser intensity was larger than 10(14)W.cm(-2), methyl acetate mainly took tunneling ionization mechanism. When the laser intensity was lower than 10(14)W.cm(-2) multiphoton ionization occurred.

Study of the Ultrafast Processes of TPP, BuPc and NtBuPc

The ultrafast processes of tetra-phenyl-porphyrin(TPP), tetra-t-butyl-phthalocyanine(BuPc) and nitro-tri-t-butyl-phthalocyanine ( NrBuPc) have been investigated using the femtosecond time-resolved fluorescence depletion method. A sharp peak of the fluorescence depletion with delay time has been observed both for TPP and BuPc. An ultrafast two-photon absorption process has been proposed to explain the sharp peak observed. A long-lived fluorescence depletion has also been observed. It is causing by the stimulated-emission-pumping process produced by the intense probe laser pulses.

The Measurement of the Ionization Potential and the Bond Energy Si(CH 3 ) 2 Cl 2

The vacuum ultraviolet photoionization spectrum of Si(CH3)(2)Cl-2 has been obtained with synchrotron radiation source. The adiabatic ionization potential of Si(CH3)(2)Cl-2 is 10.62 +/- 0.03eV (0.37eV lower than reported by PES), and the appearance potentials for Si(CH3)Cl-2(+), Si(CH3)(2)Cl+, SiCH3+ and SiCl+ are 11.25 +/- 0.03eV, 12.69 +/- 0.04eV, 15.1 +/- 0.1eV and 21.16eV +/- 0.1eV respectively. From these results, we estimate D(Si(CH3)Cl-2(+)-CH3)=0.63 +/- 0.03eV and D(Si(CH3)(2)Cl+-Cl))=2.07 +/- 0.04eV.

O( 1 D )+Si(CH 3 ) 3 Cl反应生成振动激发的OH( ν ≤3)

The vibrationally excited OH(v) from the reaction of O(D-1)+Si(CH3)(3)Cl was observed by UV lasre photolysis/FTIR emission spectroscopy. The vibrational number was only up to 3 with a ratio of 1:0.3:0 1 for v=1:2:3. Comparing this result with the similar reaction of O(D-1) + Si(CH3)(4) which OH(v) vibrational number was high up to 4 with a ration of 1:1:1:0:3 for v=1:2:3:4 under the same experimental conditions, it was found that the substitution of Cl for CH3 affected the extent of heavy Si atom blooking the energy migratio in a molecule. This results identifies the prediction that the characteristic of electrons in central atom plays an important role in intramolecular energy transfer.

A Primary Study for the Formation and Photodissociation of Aluminum Sulfide Cluster Ions

Binary cluster ions consisted of aluminum and sulfur (AlnSm+, n up to 63, m up to 94) are produced by laser ablation of a mixture of aluminum powder and sulfur powder. It was found that the formed cluster ions have a uniform increment of Al-2 S-3 in the composition. The photodissociation of the mass- selected cluster ions also show a simple dissociation channel by loss of (Al2S3)(x) (x = 1 or 3). The structural features of the cluster ions have been discussed.