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  • 學位論文

以交叉分子束及離子速度影像技術研究高振動激發態分子與惰性氣體之間的能量轉移

Energy Transfer between Highly Vibrationally Excited Aromatic Molecules and Rare Gases Using a Crossed-Beam Apparatus along with Time-Sliced Velocity Map Ion Imaging Techniques

指導教授 : 倪其焜

摘要


Abstract The energy transfer between highly vibrationally excited molecules and rare gas was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. Two molecular systems were studies. The first one is the collision between highly vibrationally excited azulene and rare gas (Kr, Ar) in a series of translational collision energies (i.e., relative translational energies 170 - 780 cm-1 for Kr and 200 - 983 cm-1 for Ar). "Hot" azulene (4.66 eV vibrational energy) was formed via rapid internal conversion of azulene initially excited to the S4 state by 266 nm photons. The shapes of the collision energy-transfer probability density functions were measured directly from the scattering results of highly vibrationally excited (hot) azulene. At low enough collision energies, azulene-Kr and azulene-Ar complexes were observed, resulting in small amount of translational to vibrational-rotational (T-VR) energy transfer. T-VR energy transfer was found to be quite efficient. On the other hand, only a small fraction of vibrational energy is converted to translational energy (V-T). We have found that substantial amount of energy transfer in the backward scattering direction due to supercollisions at high collision energies. The second one is energy transfer between highly vibrationally excited naphthalene and rare gas (Kr, Xe). The research of collision between hot naphthalene and Kr atom was in a series of translational collision energies (108~847 cm-1). Highly vibrationally excited naphthalene in the triplet state (vibrational energy: 16194 cm-1; electronic energy: 21400 cm-1) was formed via rapid intersystem crossing of naphthalene initially excited to S2 state by 266 nm photons. Similar phenomena to that of azulene were found in the energy transfer of naphthalene. In addition, the vibrational energy dependence, H and D atom isotope effect, mass effect, and the rotation effect in the energy transfer between rare gas atoms and highly vibrationally excited naphthalene in the triplet state were also investigated. Increase of vibrational energy from 16194 cm-1 to 18922 cm-1 shows almost the same phenomena in energy transfer. The energy transfer properties remain alike when H atoms in naphthalene are replaced by D atoms, indicating that the high vibrational frequency modes like C-H starches do not play important roles in energy transfer. They are not important in supercollisions, either. However, replacement of Kr atom by Xe causes the shapes of energy transfer probability density functions to change, and makes the high energy tail in the backward scattering to disappear. The probability of very large vibration to translation energy transfer, like supercollisions, is also decreased. The influence of rotation was found to be significant. As the initial rotational temperature increases, the vibrational to translational energy transfer (V®T) cross-section to translational to vibrational-rotational energy transfer (T®VR) cross-section ratio increases, but the probability to form complexes during the collisions decreases. At high initial rotational temperature, a considerable increase in the probability of large V®T(R) energy transfer, like supercollisions, have been noticed.

參考文獻


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