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Molecular dynamics simulation for hydrogen-covered Si(1 0 0):H-2×1 silicon surface was carried out to calculate the vibrational energy relaxation rates of Si–H stretches based on the Bloch–Redfield theory. The calculation gave a lifetime of 0.35 ns at 300 K, about three times shorter than the experimental result of 1.2 ns. With a reduction of force constants for the first layer reconstructed silicon dimer Si–Si stretches and Si–Si–Si bends by multiplying with 0.9 in this molecular mechanics force field, the calculation gave a lifetime of 0.51 ns, closer to the experimental result than the calculated result above. This suggests that the vibrational frequencies of first layer silicon dimers should be lower than the bulk modes. In addition, it is noted that the Si–Si–H bending frequency of 625 cm −1 on this Si(1 0 0):H-2×1 surface is lower than the 640 cm −1 on the Si(1 1 1):H-1×1 surface but the lifetime of Si–H stretches on (1 0 0) surface is shorter than (1 1 1) surface. This is in contrast to a result in a previous study for (1 1 1) surface in which the higher Si–Si–H bending frequency should result in a shorter lifetime. These results indicate that the couplings between Si–H stretches and Si–Si–H bends on the Si(1 0 0):H-2×1 surface differ significantly from the Si(1 1 1):H-1×1 surface. Besides discussion of this coupling, the isotope and thermal effects in the calculated lifetimes are reported and discussed as well.

The energetics of adsorption of non-hydrocarbon radical species on H/C(1 1 1) diamond surface and the abstraction energies of these species abstracted by hydrogen atoms, which are in excess in gas phase in the diamond thin film growth using the chemical vapor deposition (CVD) method, were examined using ab initio calculation method. Based on the calculated results for the examined species, which include H, F, OH, NH 2 , Cl, CH m X n (X=F or Cl) radicals, the tendency of incorporation of F, O, N, H and Cl atoms in the diamond thin film is discussed. The high adsorption energy and the high abstraction energy abstracted by excess gas-phase H atoms for F radicals suggest that F atom has the highest tendency to stay in the diamond thin film among the examined non-carbon atoms. In contrast, the comparable adsorption energy of Cl atom with other examined radicals except F radical, and its low abstraction energy, indicate that Cl atom possesses the least tendency to be incorporated in the diamond thin film. For O, N and H atoms, their calculated abstraction energy values suggest that the overall order of tendency of incorporation in diamond thin film is F>O>N>H>Cl. In addition, the energetically comparable adsorption energy for the CH 2 Cl radical, compared with the other examined CH m X n species, and the low abstraction energy of Cl atom support that CH 2 Cl is a good growth species in diamond CVD thin film growth.

In the present study, the energetics of H-abstraction reaction on the hydrogen-covered diamond H/C(1 1 1) surface abstracted by hydrogen atom (H), carbon (CH3, C2H), nitrogen (NH2, CN), oxygen (O, OH), and halogen-containing radicals (F, Cl, Br, CF3, CCl3) in gas phase in the diamond chemical vapor deposition process were examined using ab initio calculation. The calculations for O, F, Cl, and Br radicals gave results consistent with available experimental results. These calculated results show that F, Cl, O, OH, CN, and C2H are much stronger abstractors while NH2, CH3, CF3, and CCl3 radicals are weaker abstractors, compared with this abstraction reaction abstracted by H atoms, which is in excess in gas phase. Finally, the energy barrier heights of these examined radicals are generally correlated well with an index of electrophilicity, suggesting that this index serves as a good index to account for the ability of these examined radicals to abstract the adsorbed H atoms on H/C(1 1 1) diamond surface.

In the pres ent study, we re port the cal cu lated life times of the first hy dro gen stretch ing ex cited state on a hy dro gen-covered H/Ge(111) ger ma nium sur face us ing mo lec u lar dy nam ics sim u la tion based on the Bloch-Redfield the ory. The life time was found to be 20 mi cro sec onds at room tem per a ture, four or ders lon ger than the hy dro gen stretches on a H/Si(111) sil i con sur face. In ad di tion, the cal cu la tions for the Ge-D and Ge-T stretches gave life times in the time scale of hun dreds and tens of nano sec onds, re spec tively, at room tem per a ture. The ther mal ef fect and an ef fect of the Ge-Ge-H bend ing fre quency in the cal cu lated life times are dis cussed.

Molecular dynamics simulations of hydrogen isotope-covered silicon(111) and (110) surfaces based on the Bloch–Redfield theory were carried out to calculate the lifetimes of hydrogen isotope stretching modes on these two silicon surfaces at high temperatures. The computations gave lifetimes of 1700 and 500 ps for the Si–H stretches on H/Si(111) surface at 300 and 460 K, in good agreement with the experimental results of 950 and 550 ps, respectively. The calculations for the isotope Si–D,T stretches gave lifetimes on the time-scale of tens of picosecond at room temperature. Thermal effect and the precision of calculated lifetimes are discussed.

Molecular dynamics simulations were carried out to determine the vibrational energy relaxation rates for C–H,D,T stretches on hydrogen-, deuterium-, and tritium-terminated H,D,T/C(111) and H,D,T/C(110) diamond surfaces at high temperatures based on the Bloch–Redfield theory and the calculated power spectra of fluctuating force along C–H,D,T stretches. The lifetime of C–H stretches on H/(110) surfaces at room temperature was found to be 0.8 ps, which is much shorter than the calculated lifetime of 30 ps on a H/C(111) surface attributed to 1:3 resonance. This is due to the blueshift of the 1:2 resonance domain in the force power spectra for a H/C(110) surface. The lifetimes of C–H stretches on a H/C(110) surface and C–D,T stretches on both D,T/C(111) and D,T/C(110) surfaces, which all undergo 1:2 resonance energy relaxation, are all on the time scale of tenths of a picosecond at room temperature and are approximately inversely proportional to the square of the temperature at high temperatures. For C–H stret...

The vibrational energy relaxation rates of excited C−H,D,T stretching modes on hydrogen, deuterium, and tritium-terminated H,D,T/C(111)1×1 diamond surfaces, respectively, are calculated using the B...

The vibrational energy relaxation rate of an excited C–H stretching mode on the hydrogen‐terminated H/C(111)1×1 surface is calculated using Bloch–Redfield theory combined with classical molecular dynamics. The lifetime of an excited state is determined by the strength of the power spectrum of the force on the stretching mode at the resonance frequency. The lifetime of the first excited state is found to be 60 ps at 300 K which is shorter than the Si–H stretching mode lifetime on the H/Si(111)1×1 surface. The lifetime of the v=2 first overtone state is found to be 200 times shorter (0.30 ps). Analysis of the power spectrum of the fluctuating force along the C–H bond suggests that the mechanism of the energy relaxation for the v=1 stretching state on the H/C(111)1×1 surface is due to lower‐order interactions than on the H/Si(111)1×1 surface. The predicted fast relaxation of the overtone state may cast some doubt on the observability of that state.

A new class of hydrogen-bonded ladders based on hydrogen-bonded dimerization of oligo-alpha-aminopryidines has been demonstrated. Jorgensen's model can be successfully applied to this hydrogen-bonding system in nonpolar solvents. The results show the competitive enthalpy/entropy compensation relationship upon dimerization. Although increasing the number of hydrogen-bonding interactions would enhance the hydrogen-bonding stabilization enthalpy, this stabilization enthalpy per unit would be partially sacrificed to compensate for the entropy loss due to dimerization. These results clearly support the importance of preorganization in designing hydrogen-bonding guest-host molecules.