Novel method for accurate determination of the orientational angle of interfacial chemical groups

The common practice for determination of orientational angle of interfacial molecular groups with the interfacial sum frequency generation vibrational spectroscopy (SFG-VS) is to measure the intensity ratio between two SFG intensities at a certain vibrational frequency with different polarization directions. Because sometimes the SFG at one polarization direction is too weak to be measured accurately, this ratio usually has big uncertainty, and consequently it is impossible to obtain accurate orientation parameters. Thus the corresponding orientation angle was not accurately calculated. Through analyzing the basic relationship between the orientation angle and SFG intensity, we found that the null angle method would be suitable for such cases. The null angle measurement is simple, precise and easy to realize, therefore can greatly improve the accuracy of orientation angle. Using this method, we determined the orientation angle of the methyl group of methanol orients about 31.8 2.4 from the surface normal at the air/methanol interface, much more accurate than the previously reported value of <42. The null angle method provides a reliable experimental analytical tool for studying the orientation of the chemical group or chemical bond at interfaces.

Ionization and dissociation of CH_2I_2 and CH_2ICl in femtosecond intense field

Ionization and dissociation processes of gas molecules, CH2I2 and CH2ICl, in intense femtosecond field (1013—1015 W·cm?2), were investigated by flight time mass spectrometer, irradiated by 60 fs with 800 and 400 nm fem- tosecond laser. In the moderate intense field, CH2I2 and CH2ICl produced concerted elimination products, I2 and ICl molecules, respectively. The multiple charged ions, I2+, gen- erated in Coulomb explosion under intense femtosecond la- ser irradiation, split into three peaks in the flight time mass spectra, due to the initial kinetic energies released in the ex- plosion. The C-I internuclear distances during Coulomb ex- plosion and the kinetic energy released were estimated ac- cording to the flight time differences.

Reaction of CH radical with O2 by time-resolved FTIR spectroscopy

The reaction of CH radical with O2 has been experimentally investigated by time-resolved Fourier transform IR emission spectroscopy. CH radicals were generated by multi-photon UV laser photolysis of bromoform (CHBr3) in gaseous phase. Highly vibrationally excited product CO (v =1-12) with a near Boltzmann distribution was observed after the reaction. The vibrational temperature of CO is estimated as high as 14400(1400 K and the averaged vibrational energy is about 25.8 kcal(mol-1. The emission intensity of CO is not sensitive to the quenching gas, which indicates that there is no early barrier in the reaction of CH+O2. However, the theoretically predicted product CO2 has not been found in the experiment.

Formation, structure and properties of GeC_(n)^(±) and Ge_(2)C_(n)^(±) binary clusters

The binary cluster ions Ge2Cn+/Ge2Cn? and GeCn+ have been produced by laser ablation. The parity ef- fect is present in the negative ions Ge2Cn?, though it is not very prominent. While the experiments tell that the parity effect is totally not shown in the positive ions Ge2Cn+. An extensive theoretical investigation on GeCn/GeCn+/GeCn?(n = 1?10) and Ge2Cn/Ge2Cn+/Ge2Cn?(n = 1?9) has been carried out by density functional theory at B3LPY level. The calcula- tion shows that the low-lying states of GeCn/GeCn+/GeCn?(n = 1?10) and Ge2Cn/Ge2Cn+/Ge2Cn? (n = 1?9) are linear structure with germanium atoms locating at terminals respectively. The electronic distributions, ionization potential (IPad), 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 Ge2Cn±.