The interactions of sub-cycle and single-cycle pulses with two- or three-level quantum systems are studied, respectively. For the two-level quantum system, two cases in which the carrier frequency of pulses is in resonance and far from resonance with the atom are analysed. The ultrafast complete population transfer can be obtained. The sub-cycle pulse with a far off-resonant carrier frequency is found to be more suitable for the population transfer. The relation between the area of pulses and population transfer is clarified in the sub-cycle and single-cycle domain. For the Lambda-type three-level quantum system, more than 90% of population transfer can be achieved from one level to another. The scheme is insensitive to the variation of the laser parameters such as the peak Rabi frequency and the carrier frequency for both two- and three-level quantum systems.

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Abstract. A dressed-state perturbation theory beyond the rotating wave approximation (RWA) is presented to investigate the interaction between a two level electronic transition of the polar molecules and a quantized cavity field. Analytical expressions can be explicitly derived for both the ground-and excited-state-energy spectrums and wave functions of the system, where the contribution of permanent dipole moments (PDM) and the counter-rotating wave term (CRT) can be shown separately. The validity of these explicit results is discussed by comparing with the direct numerical simulation. Comparing to CRT coupling, PDM results in the coupling of more dressed states and the energy shift proportional to the square of the normalized permanent dipole difference, and a greater Bloch-Siegert shift could be produced in giant dipole molecule cavity QED. In addition, our method could also be extended to the solution of two-level atom Rabi model Hamiltonian beyond the RWA.

The bond dissociation energy (BDE) of syndiotactic polystyrene(s-PS) was calculated by using four density functional theory methods, which were M062X, B3LYP, B3P86, BH and HLYP with different LANL2DZ, 6-31G(d), 6-31G(d, p), and 6-311++G(d, p) basis sets. The influence of these computational methods on the accuracy of the BDE of s-PS was analyzed. It was found that the BDE had a higher accuracy at B3P86/6-31G (d, p) level than other methods, and B3P86/6-31G (d, p) spent more less time to calculate the bond dissociation energy of s-PS, and the average of the C-C bonds’ BDE values calculated by B3P86/6-31G (d, p) is about 8.3 kJ/mol lower than the experimental value (310.0 kJ/mol), which is derived from the i-bond database. Besides, the bond dissociation energy values of the C-C bonds computed by M062X/LANL2DZ, B3LYP/6-31G(d), M062X/6-31G(d), B3LYP/LANL2DZ and BH and HLYP/6-311++G(d, p) methods were as follows: 330.8 kJ/mol, 345.3 kJ/mol, 283.2 kJ/mol, 267.6 kJ/mol, 267.4 kJ/mol. The calculation conclusion is drawn that different calculation methods with the same basis set have an obvious influence on the result of BDE values’ calculation. Finally, based on the calculation of bond dissociation energy of polystyrene, three possible reaction paths of polystyrene pyrolysis are designed to analyze the influence of bond dissociation energy on polystyrene pyrolysis.

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