Effect of temperature on the CO2 splitting rate in a DBD microreactor.

A novel plate-to-plate dielectric barrier discharge microreactor (micro DBD) has been demonstrated in CO2 splitting. In this design, the ground electrode has a cooling microchannel to maintain the electrode temperature in the 263-298 K range during plasma operation. A small gap size between the electrodes of 0.50 mm allowed efficient heat transfer from the surrounding plasma to the ground electrode surface to compensate for heat released in the reaction zone and maintain a constant temperature. The effect of temperature on CO2 conversion and energy efficiency was studied at a voltage of 6-9 kV, a frequency of 60 kHz and a constant CO2 flow rate of 20 ml min-1. The CO2 decomposition rate first increased and then decreased as the electrode temperature decreased from 298 to 263 K with a maximum rate observed at 273 K. Operation at lower temperatures enhanced the vibrational dissociation of the CO2 molecule as opposed to electronic excitation which is the main mechanism at room temperature in conventional DBD reactors, however it also reduced the rate of elementary reaction steps. The counterplay between these two effects leads to a maximum in the reaction rate. The power consumption monotonously increased as the temperature decreased. The effective capacitance of the reactor increased by 1.5 times at 263 K as compared to that at 298 K changing the electric field distribution inside the plasma zone.

Spectroscopic investigation of the molecular vibrations of 1,4-dihydronaphthalene in its ground and excited electronic States.

A comprehensive spectroscopic study of 1,4-dihydronaphthalene (14DHN) has been carried out for its ground and S(1)(pi,pi*) electronic states using infrared, Raman, ultraviolet, and laser-induced fluorescence (LIF) spectroscopic techniques. The experimental work was complemented by ab initio and DFT calculations. For the ground state excellent agreement between observed and calculated values was attained. For the S(1)(pi,pi*) excited state 19 of the vibrational modes were clearly determined and excited vibronic levels for a number of these were also identified. A detailed energy map for the low-frequency modes in both electronic states was established. 14DHN is very floppy in its S(0) ground state but less so in its excited state. The floppiness relaxes C(2v) selection rules for the S(0) state.

Ultraviolet cavity ringdown spectra and the S1(n,pi) ring-inversion potential energy function for 2-cyclohexen-1-one-d0 and Its 2,6,6-d3 isotopomer.

The cavity ringdown spectra of 2-cyclohexen-1-one (2CHO) and its 2,6,6-d3 isotopomer (2CHO-d3) have been recorded in the spectral region near their S1(n,pi)<--S0 band origins which are at 26,081.3 and 26,075.3 cm-1, respectively. The data allow several of the quantum states of nu39, the ring inversion, to be determined for both the ground and excited electronic states. These were utilized to calculate the one-dimensional potential energy functions which best fit the data. The barriers to inversion for the S0 and S1(n,pi) states were found to be 1,900 +/- 300 and 3,550 +/- 500 cm-1, respectively. Density functional theory calculations predict values of 2,090 and 2,265 cm-1, respectively.

Vibrational spectra, DFT calculations, unusual structure, anomalous CH2 wagging and twisting modes, and phase-dependent conformation of 1,3-disilacyclobutane.

Our previously published infrared and Raman spectra of 1,3-disilacyclobutane (13DSCB) and its 1,1,3,3-d4 isotopomer have been reexamined and partially reassigned on the basis of DFT and ab initio calculations. The calculations confirm previous microwave work that the CSiC angles in the ring are unexpectedly larger than the SiCSi angles. This may arise from the partial charges on the ring atoms. The calculations are in excellent agreement with the observed spectra in both frequency and intensity. They also demonstrate that this molecule has CH2 wagging and twisting vibrations with frequencies below 1000 cm-1, about 200 cm-1 lower than expected. These unprecedented low values can be explained by the decreased slope in the potential energy curves for these vibrations as the sideways motions of the CH2 groups result in attractive forces between the positively charged hydrogens on the carbon atoms and the negatively charged hydrogens on the silicon atoms. The theoretical calculations also confirm the previous conclusions that the individual molecules (vapor) have C2v symmetry whereas in the solid the molecules become planar with D2h symmetry. The vibrational coupling between the ring-angle bending mode and the SiH2 in-phase rocking, which is present for the C2v structure, is forbidden for D2h and hence disappears.