Yi-Jen Wang

Hydrogen chemisorption and thermal desorption on the diamond C(111) surface

Temperature programmed desorption (TPD) and low energy electron diffraction (LEED) were utilized to study the interaction of atomic hydrogen with single crystal diamond C(111) surface. From isotherm and isostere analysis of TPD spectra acquired at various sample heating rates ranging from 0.6 K/s to 30 K/s, the kinetic parameters were extracted. It is found that molecular hydrogen desorption from the C(111) surface exhibits the first-order kinetics. This result is confirmed by no apparent shift in peak temperatures of TPD spectra for hydrogen coverage above 0.2 ML. At lower coverage regime, the isothermal desorption experiment also indicates the first-order desorption kinetics. A nearly coverage-independent activation energy of (3.7±0.1) eV and a prefactor of (9.5±4.0)×1013 s−1 are obtained except at relatively low coverages (below ∼0.2 ML). In addition, the half-order LEED spots intensity decreases linearly with increase of the hydrogen coverage and drops to zero at ∼0.5 ML. These results are interpreted...

Rotational analysis of bands of the à - X̃ transition of the C3Ar van der Waals complex.

Rotational analyses have been carried out for four of the strongest bands of the Ã-X̃ transition of the C3Ar van der Waals complex, at 393 and 399 nm. These bands lie near the 02(-)0-000 and 04(-)0-000 bands of the Ã(1)Πu-X̃(1)Σ(+) g transition of C3 and form two close pairs, each consisting of a type A and a type C band of an asymmetric top, about 4 cm(-1) apart. Only K″ = even lines are found, showing that the complex has two equivalent carbon atoms (I = 0), and must be T-shaped, or nearly so. Strong a- and b-axis electronic-rotational (Coriolis) coupling occurs between the upper states of a pair, since they correlate with a (1)Πu vibronic state of C3, where the degeneracy is lifted in the lower symmetry of the complex. Least squares rotational fits, including the coupling, have given the rotational constants for both electronic states: the van der Waals bond lengths are 3.81 and 3.755 Å, respectively, in the ground and excited electronic states. For the ground state our new quantum chemical calculations, using the Multi-Channel Time-Dependent Hartree method, indicate that the C3 unit is non-linear, and that the complex does not have a rigid-molecule structure, existing instead as a superposition of arrowhead (↑) and distorted Y-shaped (Y) structures.

Analysis Of Bands Of The 405 Nm Electronic Transition Of C3ar

Bands of the C3Ar complex can be observed near almost all the bands of the ÃΠu X̃Σg transition of C3. The strongest bands of C3Ar form close-lying pairs. Rotational analyses have been carried out for the bands at 25025 and 25029 cm−1(near the 02−0-000 band of C3) and 25426 and 25430 cm−1(near the 04−0-000 band). Each pair consists of a type A and a type C band of an asymmetric top, where the upper states interact by b-axis Coriolis coupling; this represents the lifting of the degeneracy of the Π state in the lower symmetry of the complex. Only K = even lower state levels are found, showing that C3Ar has the shape of a distorted letter T. The Ar atom lies 3.82 Å from the centre of mass of the C3 part. Emission spectra have been recorded and lifetimes measured for several C3Ar upper state levels. The assignment of the emission bands is complicated by significant intramolecular relaxation in the upper states, which populates mainly the lowest level of each local potential minimum of the upper state; however the variation of the upper state well depth (binding energy) with vibrational quantum number can then be determined.