229 research outputs found
A study of left-turn-on-red (LTOR) traffic control at signalized junctions in Singapore
No full textThe research study evaluated LTOR performance in Singapore on road user behaviours and their interactions, delay saving, and safety. A literature survey provided pertinent LTOR/RTOR experiences overseas. Field data were collected in 2001/02 from 5 LTOR junctions and 4 non-LTOR junctions via on-site observations.Master of Engineering (CEE
[[alternative]]Theoretical Studies of Isomerization Reactions of 2-Pentoxy Radical and Its Derivatives in the Troposphere
No full text[[abstract]]Abstract
This thesis deals with the calculation of isomerization reactions of 2-pentoxy radical and its derivatives by density function theory. All of the local minimum structures are optimized with 6-31G and 6-311++G** basis set at the levels of HF and B3LYP. There are five sections rendered here.
Section 1: We study the intramolecular hydrogen transfer from five different positions of carbon of the 2-pentoxy. There are five paths of hydrogen transfer discussed, which include the transition structure of 3-, 4-, 5-, and 6-member ring. The results indicate that the rate constant of 6-member ring calculated at the B3LYP/6-311++G** level is very close to the experimental value. The rate constant is 1.25×105(s-1). The order of the energy barriers among five possible pathways are 3-, 4- >5- >6- member ring. The energy barrier of 6-member ring is 8.63 kcal/mol. The ring strain of the transition state surely dominates the energy barrier of the intramolecular hydrogen transfer.
Section 2: We study the double bond isomerization reactions at these series reactions. The ring strain of the transition state is not the only influence factor on the barrier of the double bond reaction. The second factor is the stability of each product. The pent-1-ene-4-oxy radical undergoes isomerization by 1,3-hydrogen shift via a lower energy barrier than that of 2-pentoxy radical. The energy barrier is 20.89 kcal/mol. The energy barrier of pent-2-ene-4-oxy radical isomerization via a six-member ring transition state, 6.9 kcal/mol, is also lower than the analogous process of 2-pentoxy radical.
Section 3: We study substitution effect of isomerization of 2-pentoxy radical. In this section, we only discuss isomerization proceeding through a 6-member ring. The lowest barrier of these reactions is 5-methyl-2-hexoxy radical. The energy barrier is 3.77 kcal/mol. We find that the relative energy of the product is an important factor relating to the barrier-height of these isomerization reactions.
Section 4: We study isomerization reactions of R(NH)?and RS?proceeding through 4-,5-, and 6-member ring. The reactions of R(NH)? are similar to the reactions of RO?, but the reactions of RS? are quite different. The barrier of the reactions of RS? via 5-member ring is lower than that via 6-member ring.
Section 5: We summarize two important factors on the barriers of isomerization reactions of alkoxy radicals and its derivatives. One is ring strain of the transition structure, and the other is the relative energy of the product.
[[alternative]]Theoretical Study of Intra-molecular Hydrogen Transfer of Formyl radical and Its complexes
No full text[[abstract]]Abstract
This dissertation deals with the calculation of intramolecular hydrogen transfer of formyl radical and its derivative complexes by ab initio and DFT methods. Each local minimum and its corresponding TS are fully optimized with 6-311G** and 6-311++G** basis sets at the levels of HF、MP2 and B3LYP. Relative energies of species are finally evaluated at B3LYP、MP2 or G2 theory. There are five sections rendered here.
Section 1: First of all, we study the intramolecular hydrogen transfer of the formyl radical (HCO), which is a trial and used as a comparison to the data in the literature. Results indicate that structure of HCO calculated by DFT method with B3LYP/6-311++G** level is very close to the experimental values. The result is RC-O=1.174 A、RC-H=1.125 A and ∠HCO=124.5°. With respect to previous studies, DFT method takes shorter time in calculating and more accurate in the geometry structure. However in other levels, the calculated barrier is about 64~69 kcal/mol for the intramolecular hydrogen transfer. The binding energy of H-CO bond calculated by G2 method including BSSE correction is –13.72 kcal/mol.
Section 2: Intramolecular hydrogen transfer of complex of HC(O)O2 is studied in this section. In ground state, formylperoxy radical is found to have two isomers, among which are Z and E forms. There are three different product channels in performing intramolecular hydrogen transfer onto the two isomers. The first product is like a carbene structure having higher energy than the reactants (HCO+O2) by 40 kcal/mol. The second channel produces HO2+CO with activation energy of 0.201 kcal/mol at 298 K, B3LYP/6-311++G** level. The activation energy of the third product channel (OH+CO2) is 9.5 kcal/mol. We concluded that the barrier of intramolecular hydrogen transfer is affected by the strain of the transition structure.
Section 3: We studied the intramolecular hydrogen transfer of the Nitrosylformate complex HC(O)NO2. There were four paths of hydrogen transfer discussed, which include the transition structure of 3-, 4-, or 5- member ring. It is found that the barrier of 3- member ring is the highest and that of 4- member ring is almost equal to the barrier of 5- member ring. Because of different structure and distance between the original atom (C) and the target atom (O), 5-member ring has a higher energy barrier. The strain of the transition state surely dominates the energy barrier of the hydrogen transfer.
Section 4: The intramolecular hydrogen transfer of HC(O)NO3 complex is also studied. The binding energy of HCO and NO3 is quite high. The resultant product (HNO3) is also observed by experiment.
Section 5: Finally, we focused our study on the intramolecular hydrogen transfer of HC(O)O3 complex. There are three isomers of HC(O)O3. The first isomer (complex I) has no barrier for the hydrogen transfer. The splitting products of the complex, II and III, after hydrogen transfer are CO+HOOO and CO+HO3, respectively, their energy differences are quite large.
[[alternative]]The Stable Structures of Cluster ion
No full text[[abstract]]利用高壓氣體由噴嘴(nozzle)噴入超高真空,由於絕熱膨脹使氣體分子的
溫度劇降而凝結成分子團簇(molecular clusters)。利用一部配有雷射多
光子游離(laser based multiphoton ionization)和電子碰撞游離(
electron impact ionization)裝置的飛行時間質譜儀(time-of-flight
mass spectrometer),來研究離子態分子團簇。由所得的飛行時間質譜來
分析各種離子態分子團簇所呈現的譜線強度,可得知離子態分子團簇的穩
定結構。本論文報導argon 、ammonia 、及carbon disulfide等的離子態
分子團簇的研究成果。
Neutral clusters,produced via supersonic expansion,are
subjected to multiphoton ionization by pulsed laser or electron
impact ionization by electron gun.The products of cluster ions
are investigated using a time-of-flight mass spectrometer.The
strong peaks on mass spectra are related to particularly stable
structures due to closely packings or special types of bondings.
Based on the analysis of their ion intensity distributions,
stable structures of cluster ions are deduced.In this paper,
cluster ion systems of argon、ammonia、 and carbon disulfide
are investigated and reported.
Neutral clusters,produced via supersonic expansion,are
[[alternative]]Theoretical Studies of Tropospheric Reactions of Methy tert-Butyl Ether and Its Derivative Alkoxy Radicals
No full text[[abstract]]This thesis deals with the calculation of tropospheric reaction of methyl tert-butyl ether (MTBE) and its derivatives by density functional theory at B3LYP/6-311++G(d,p) level. To find the rules of alkoxy radicals in the reaction of atmosphere, we studied several C1-C5 alkoxy radicals of different structures in the reactions and analyzed their relationships. There are three major sections for the reactions we studied and they are rendered here.
Section 1 We study the hydrogen abstraction reaction with hydroxyl radical and the subsequent rearrangements and fragmentations of MTBE in atmospheric condition. The result of inaccurate energy value and severe spin contamination at MP2/6-31+G(d) level makes us switch to B3LYP/6- 311++G(d,p) level of calculation. There are two possible positions of MTBE that hydroxyl radical can abstract the hydrogen atom and our results indicate that they are competitive, and the final products should be t-butyl alcohol (TBA), formaldehyde, isobutene and methanol, which agree well with the experimental result.
Section 2 Two derivatives of alkoxy radicals (A1 and B1) are studied in this section. We investigate their decomposition, isomerization and oxidation reactions, which are major reaction processes for general alkoxy radicals in the atmosphere. We conclude that the oxygen atom in MTBE may be a major factor that change the reaction tendency significantly We also investigate A1 and B1 to react with other important molecule in atmosphere such as N2, NO, and CO. The result indicates that NO is more active than O2 toward forming stable intermediates.
Section 3 There are some good relationships between energy barriers and reaction energies for primary and secondary alkoxy radicals in carrying out decomposition reaction. We also study the unsaturated alkoxy radicals in the decomposition reaction, and find that the position of double bond will affect energy barrier and selectivity significantly. Analogous to the saturated alkoxy radicals, the unsaturated ones also have good linear relationship between energy barriers and reaction energies. The natural population analysis (NPA) in 1,5 H-shift isomerization reaction indicates that alkyl substitution on H-transferred carbon atom could decrease the energy barrier. The oxidation reaction with oxygen is the most important channel in small alkoxy radicals (<C4), in contrast, the isomerization reaction becomes dominant in large alkoxy radicals, partly because of larger steric effect and much smaller isomerization barriers.
[[alternative]]Theoretical Study of SO2 Formation in the Reaction of CH3S Radical with NO2，O3，O2 and HO2 in the Gas Phase
No full text[[abstract]]This thesis deals with the calculation of tropospheric reaction of methylthiyl radical(CH3S) with NO2，O3，O2 and HO2 to check the formation of SO2 by ab initio theory at MP2/6-311G(d) level. There are four major sections to describe the reaction mechanisms.
Section 1: We study the reaction between methylthiyl radical and nitrogen dioxide(NO2) in the gas phase . The reaction proceeds with the participation of NO2 by twice or three times to produced sulfur dioxide. The formation energy is relatively large and the product is stable. Therefore, we think the reaction of methylthiyl radical with nitrogen dioxide to produce sulfur dioxide is very possible.
Section 2: We studied the reaction of CH3S with O3.We found out that with the participation of O3 two times it is possible to form CH3SO2 and than dissociated to SO2.We detect the reaction of methylthiyl radical with ozone twice to produce CH3SO2.After that, we through the thermal decomposition of CH3SO2 and we can get SO2.
Section 3: We studied the reaction of CH3S+O2. We found out that the cleavage energy of O-O bond of intermediate is quite high. As a consequence, it is not possible for the formation of SO2 via this process.
Section 4: We studied the reaction of CH3S+HO2.We found out that the intermediates D2 and D5 are very stable, and it seems not possible to proceed further to produce SO2 in this reaction.
[[alternative]]Ab Initio Theoretical Calculation to Study the Formations,
No full text[[abstract]]利用 Ab Initio 理論計算探討 Li3OH 及 Na3OH 分子的生成及穩定性，
發現 Li3OH 分子有三種異構物，能量由低至高依次為 C2VⅡ、C2VⅠ、C3
V,Li2 分子與 LiOH 分子碰撞可生成 Li3OH 分子的 C2VⅠ結構，同時放
出 48.36 kcal/mol 的熱量， LiH 分子與 Li2O 分子碰撞可生成 C2VⅡ
結構，同時放出 59.30 kcal/mol 的熱量，由 C2VⅠ 結構轉換至 C3V 結
構僅須克服 9.89 kcal/mol 的能量障礙，而由 C3V 結構轉換至 C2VⅡ結
構則須克服 21.99 kcal/mol 的能量障礙，同樣的情形也存在於 Na3OH
分子，但最大的不同是 Na3OH 分子三種異構物的能量高低順序恰與 Li3
OH 分子相反。 Li4O 及 Na4O 分子均具有 Td 及 C2V 兩種結構，且都是
以 Td 結構較穩定，Li4O 分子的 Td 結構比 C2V 結構穩定 15.17 kcal/
mol，而 Na4O 分子的 Td 結構比 C2V 結構穩定 18.13 kcal/mol，Li4O
分子由 Td 結構轉換至 C2V 結構的活化能為 17.77 kcal/mol，而 Na4O
分子由 Td 結構轉換至 C2V 結構的活化能為 19.37 kcal/mol，兩者轉換
過程中的過渡狀態均是以氧原子位於頂點的 C3V 傘狀結構。 Li4OH 分子
有三種穩定異構物，其中能量最低的結構是以 O-H 為主軸的 C2V 對稱結
構，此結構可視為 H 原子加在 Li4O (Td) 的 Li-O-Li 角平分線上，但
氫原子不與氧原子鍵結，而與鄰接的兩個鋰原子形成 Li-H-Li 三中心鍵
，Li4OH 分子的 HOMO 是 A1 對稱，此軌域提供鋰原子間的過金屬鍵，
將 Li4OH分子游離一電子成為 Li4OH+ 離子的游離能為 91.96 kcal/mol
，Li4OH+ 離子也是 C2V 對稱，但由於過金屬鍵的消失，Li-Li鍵長由
Li4OH 分子中的 2.478 A 增至 Li4OH+ 離子中的 2.985 A 。
The production of Li3OH molecule due to the collision process
of Li2 and LiOH or LiH and Li2O were investigated theoretically.
The association reaction energies for these processes are
-48.36 kcal/mol and -59.30 kcal/mol each other. There are
three stable structures ( C3V, C2VⅠ and C2VⅡ) for Li3OH
molecule.The global minimum structure has C2V symmetry with H
and two Li atoms forming a 3-centered bond. The energy barrier
of inter-conversion between C2VⅠ and C3V structure is 9.89
kcal/mol. The energy barrier of inter-conversion between C3V
and C2VⅡ structure is 21.99 kcal/mol. And the transition state
is also determined. There are two stable structures (Td and C2
V) for Li4O molecule and the Td structure is calculated to be
lower in energy. The energy barrier of inter-conversion
between these two structures is calculated to be 17.77 kcal/mol
and the transition state is also determined. Fourteen possible
Li4O structures Have been studied. Among them the structure
with the lowest energy has C2V symmetry with H and two Li
atoms forming a 3-centered bond. The O-Li-H-Li stays in the
same plane with O-H axis bisecting the Li-O-Li angle. The two
Li-O-Li angles are 90.5o and 76o which are distored quite a lot
from Li4O (Td) structure if we considered Li4OH being formed
from Li4O (Td) + H . The HOMO of ground state Li4OH has A1
symmetry. It contributes considerable metal-metal bonding
between Li-Li bonds. The ionization energy ( Li4OH → Li4OH+ )
is 91.96 kcal/mol. The ground state structure of Li4OH+ also
has C2V symmetry. However; the metal-metal bonding between Li-
Li was weakened drastically which makes the Li-Li bond length
increase from 2.478 A in Li4OH to 2.985 A in Li4OH+. Other
possible structures of Li4OH and their ionization counterpart
( Li4OH+ ) are also being carefully studied.
The production of Li3OH molecule due to the collision process
[[alternative]]theoretical study of reaction mechanisms of some simple organic molecules
No full text[[abstract]]We carried out theoretical studies for two important reactions involving HNCO peptide bond: 1. the methylation of Hydroxamic Acid (RC(=X)NHOH, X=O、R=H) and its derivatives (X=S、R=CH3,Cl,CHCH2) with diazomethane , and 2. the thermal deamination and denitrosation of N-Nitrosoamides . The descriptions are following:
Part 1： There are seven possible pathways of methylation of (Z)HAs to generate O-alkylation and N-alkylation products. Path Z7 generating (Z)O,O-dimethylhydroxamates 9 has the lowest energy barrier 17.24 kcal/mol. The reaction between HAs and CH2N2 results in predominant formation of product 9 strictly high-site selective. When the substitutents of CH3, Cl and CHCH2 are added, the energy barrier of pathways and the site selection of product will be affected. The probability for the formation of (Z)N,O-dimethylhydroxamates 6 will be increase.
There are six possible pathways in the E-form Has methylation. Path E5、E6 generate (E)O,O-dimethylhydroxamate 24 , with the energy barriers, 22.85 kcal/mol, and 23.06 kcal/mol respectively. The substituents CH3, Cl and CHCH2 have little effect to the site-selectivity of the products except the Cl-substituent changes the rate-determine step. The production of (E)N,O-dimethylhydroxamates 27 has higher energy barrier.
Part 2： The similar methylation reaction of thiohydroxamic acid is investigated and the result compared with that of hydroxamic counterparts. We found that the relative energies、structures of transition state and the pathways of reaction were affected by two major factors: the size and the electronegativity of O and S atom. However products of Z and E isomers of SHAs also have high site-selectivity , with N-methyl product obtained at higher barrier, similar to Has counterparts.
Part 3： We studied theoretical the thermal decomposition of N-Nitrosoamides and designed two isodesmic reaction to understand the substitutions effects on the stability of the reactant and transition state . We found that the substitution at the different sites (N and C) of N-Nitrosoamides led to very different results. The silyl substituent at C-site even followed different pathway of decomposition.
The thermal decomposition of N-Nitrosoamides in acidic condition may undergo deaminative (loss of N2) and denitrosative (loss of NO+) two competitive pathways. According to our result, we may understand how the acidity, temperature and added nucleophilicity affect reaction barriers.
The Challenges of Autonomous Vehicles In Malaysia: From The Perspective Of Motorcycle Traffic Crashes: DOI: https://doi.org/10.33093/ijomfa.2025.6.1.3
No full textThe Level 3 autonomous vehicle (AV) is now a reality on the public roads. While the emergence of AV is to eliminate the traffic crashes due to human error by 90%, the unexpected or errant drivings on the roads would, however lead to traffic crashes as the operation of AVs are depending on the artificial intelligence, which involve constantly teaching the computer to learn. In Malaysia, motorcycle fatalities accounted for about 60% of the total traffic fatalities, of which the majority of the fatalities were due to human errors. - The presence of motorcyclists in the traffic stream then becomes challenge to the operation of AVs due to the unpredictable and inconsistent behaviour of the motorcyclists. Therefore, to ensure the safe deployment of AVs in the country, this study is taken to unveil the characteristics of certain traffic crashes involving motorcyclists. The findings show that as high as 40% of the motorcycle casualties were due to the motorcycles’ faults. Careless driving, speeding, dangerous overtaking and turning are among the causal factors. The findings shed important insights to AV software programm developers in the process of detecting and processing necessary response plans. Besides, the car makers can also propose more crashworthiness vehicles from the perspective of vulnerable road users.
The Challenges of Autonomous Vehicles In Malaysia: From The Perspective Of Motorcycle Traffic Crashes
No full textThe Level 3 autonomous vehicle (AV) is now a reality on the public roads. While the emergence of AV is to eliminate the traffic crashes due to human error by 90%, the unexpected or errant drivings on the roads would, however lead to traffic crashes as the operation of AVs are depending on the artificial intelligence, which involve constantly teaching the computer to learn. In Malaysia, motorcycle fatalities accounted for about 60% of the total traffic fatalities, of which the majority of the fatalities were due to human errors. - The presence of motorcyclists in the traffic stream then becomes challenge to the operation of AVs due to the unpredictable and inconsistent behaviour of the motorcyclists. Therefore, to ensure the safe deployment of AVs in the country, this study is taken to unveil the characteristics of certain traffic crashes involving motorcyclists. The findings show that as high as 40% of the motorcycle casualties were due to the motorcycles’ faults. Careless driving, speeding, dangerous overtaking and turning are among the causal factors. The findings shed important insights to AV software programm developers in the process of detecting and processing necessary response plans. Besides, the car makers can also propose more crashworthiness vehicles from the perspective of vulnerable road users
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