Hamiltonian description and 6D calculations on the ammonia vibrational levels

In this work, a Hamiltonian formalism and a 6D vibrational calculation procedure is described and implemented, designed for the exploration of vibrational motion in ammonia (and any XH₃ molecule). The 6D potential energy surface of ammonia was modelled in simple analytical form (including the inversion potential) at the planar, totally symmetric (D_3h) reference configuration. Using the described method (which is an adaptation of the formalism, previously developed and applied to benzene), 6D calculations were carried out on the vibrational level system of ammonia ¹⁴NH₃, at the lower levels of vibrational excitation. On the basis of the satisfactory agreement between the calculated and the experimentally measured vibrational frequencies, the values of some important harmonic and anharmonic force constants, characterizing the ammonia PES were determined.     

Foreign gas broadening of an IR absorption line of formaldehyde

The theory of nuclear spin state relaxation of symmetrical molecules like formaldehyde contains a collision time t_c that is interpreted as time between rotationally inelastic molecular collisions. This time traditionally is determined from measurements of pressure broadening of spectral lines. In order to test whether these collision times, which determine spin relaxation rate constants and line broadening coefficients, respectively, are the same or at least related to another, we have performed systematic measurements of the broadening of an IR line of formaldehyde by other gases of different pressures.     

On the study of the vibrational energy levels of Arsine molecule

We compare two formalisms applied to the vibrational modes of the molecule of AsH₃ of C_3v molecular symmetry group. Indeed, the close stretching modes of this molecule may be considered as those of a three-dimensional oscillator whereas the bending modes may be considered either as a one-dimensional oscillator of symmetry A₁ and a two-dimensional oscillator of symmetry E or as an approximate three-dimensional oscillator. So, we have applied the U(p + 1) formalism to the both stretching and bending modes and introduced coupling terms acting on an appropriate coupled vibrational basis through a local mode formalism. We have then compared the result of our fitting with those obtained with the coupling of a local mode formalism adapted to the stretching vibrations with a normal mode formalism for the bending ones. Finally we compare our results with other methods recently proposed in the literature.     

聚二乙炔链振动谱的研究

将聚二乙炔主链简化为有限的一维复式碳原子链,利用经典的晶格动力学方法研究了其色散关系.聚二乙炔链色散关系曲线由一支声学模和三支光学模组成,它们在波矢为零处及Brillouin zone(BZ)边界处拉开了间隙,弹性力常数的变化将显著地改变带宽和能隙.     

用代数模型研究非刚性HCP分子的振动谱

提出一种研究非刚性HCP分子的高激发非线性振动的代数哈米顿量,它在极限条件下退化为传统的用谐振子算子表示的模型,拟合观测的实验数据表明,代数模型比传统模型较好地描述了这些数据．     

Efficient non-resonant intermolecular vibrational energy transfer

Molecular excited vibrational states are metastable states and we incorporate their finite lifetimes into the theory of vibrational energy transfer between weakly interacting molecules, i.e., at internuclear distances at which they do not have a chemical bond. Expressions for the effective lifetime of an initially vibrationally excited molecule in the presence of a neighbouring molecule are derived in closed form. These expressions allow one to analyse the physics behind the energy transfer. It is shown that due to different finite lifetimes of the isolated excited molecules, a very efficient vibrational energy transfer can take place between them even if their energies are rather off-resonance. Examples are discussed.     

An algebraic approach to the study of the vibrational spectra of HCN

Using Lie algebra the vibrational energy levels of HCN were calculated using the local Hamiltonian for 35 vibrational bands. A comparative study was made with earlier results.     

Model for vibrational relaxation: Pure-dephasing and depopulation

The three dominant mechanisms giving major contributions to vibrational relaxation in molecular systems are (a) pure dephasing, (b) depopulation (or energy relaxation), and (c) resonant transfer. Here (c) is not considered but the effects due to thesimultaneous occurrence of (a) and (b) are treated within a stochastic model. In dealing with (a), the vibrational frequency is assumed to undergo random uncorrelated ‘jump’, due to fluctuations in the environment of the active molecule between a continuous set of values. The ensuing results are somewhat different from those of the commonly used Kubo model of vibrational dephasing, especially at long times and appear to be better suited in interpreting certain experimental data. The model is next extended to include the simultaneous occurrence of (b). The calculation leads to two important conclusions: (i) the lineshape is not just the convolution of those due to (a) and (b), and (ii) the lineshape is asymmetric, if the intermolecular interactions are not isotropic.     

Sum-frequency vibrational spectroscopic studies of Langmuir monolayers

Surface-sensitive sum-frequency vibrational spectroscopy (SFVS) has grown into a most viable analytical tool to investigate Langmuir monolayer systems. It has been successful in deducing information on many key properties of Langmuir films not obtainable by other techniques. This review gives a survey on the current status of SFVS studies of Langmuir monolayers with emphasis on the structures of both surfactant monolayers and interfacial water under various circumstances.     

Synthesis and formaldehyde sensing performance of LaFeO3 hollow nanospheres

Metal oxide semiconductors with hollow structure and morphology have attracted considerable attentions because of their promising application on gas sensors. In this paper, LaFeO₃ hollow nanospheres have been prepared by using carbon spheres as templates in combination with calcination. Based on the observation of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and transmission electron microscope (TEM), the structure and morphology of the products were characterized. It has been revealed that as-prepared LaFeO₃ samples have a uniform diameter of around 300 nm and hollow structures with thin shells of about 30 nm consisting of numerous nanocrystals and nanopores. Owing to the hollow and porous structure, large surface area and more surface active sites, the sensor based on LaFeO₃ hollow nanospheres exhibited high response, good selectivity and stability to formaldehyde gas (HCHO). It suggests that the as-prepared LaFeO₃ hollow nanospheres are promising candidates for good performance formaldehyde sensor.     

Algebraic approach to the study of excited vibrational states

The algebraic method of perturbation theory for eigenvalues and eigenvectors is used for the theoretical study of molecular parameters of excited vibrational states. Within the framework of this method, formulas for higher-order elements of the vibration form tensors are obtained. They can be used for the study of changes in intramolecular parameters of vibrations and the anharmonic coefficients of kinematic interaction.     

光谱法测定室内空气中甲醛浓度

为了对甲醛的浓度进行快速而有效的检测，设计了一套光栅式光谱检测系统。该系统主要包括光学系统、光电信号采集系统和计算机处理系统。系统硬件电路包括前置放大滤波电路、A/D转换电路及单片机的数据采集和发送电路。对酚试剂分光光度法测定空气中甲醛浓度的实验条件进行了研究，分析了影响实验结果的因素，得出了光谱检测实验的实验结果，并对相关结论进行了分析和论证。通过所设计的系统，可直接测出甲醛分析液的透射光光谱，从而得出相应的甲醛浓度。     

A DFT study of formaldehyde adsorption on functionalized graphene nanoribbons

Density functional theory (DFT) based ab initio calculations were done to monitor the formaldehyde (CHOH) adsorptive behavior on pristine and Ni-decorated graphene sheet. Structural optimization indicates that the formaldehyde molecule is physisorbed on the pristine sheet via partly weak van der Waals attraction having the adsorption energy of about −15.7 kcal/mol. Metal decorated sheet is able to interact with the CHOH molecule, so that single Ni atoms prefer to bind strongly at the bridge site of graphene and each metal atom bound on sheet may adsorb up to four CHOH. The findings also show that the Ni decoration on graphene surface results in some changes in electronic properties of the sheet and its E_g is remained unchanged after adsorption of CHOH molecules. It is noteworthy to say that no bond cleavage was observed for the adsorption of CHOH on Ni-decorated graphene.