A refined estimate of the bond length of methane

The atmospheric reaction of H₂S with Cl was investigated using high level ab initio calculations and Canonical Variational Transition State Theory (CVTST). The adduct formation step is the dynamical bottleneck, and the rate constant was calculated to be 1.2 × 10^?9 cm³ molecule^?1 s^?1, which is around ten times greater than the upper experimental value. Additional ab initio classical trajectory calculations show that the adduct formed in the initial collision can easily dissociate, recrossing the variational transition state. The stabilization of this species depends on the vibrational excitation of H₂S molecule, which requires an almost collinear SH-Cl collision. These dynamical effects provide an explanation for the substantial error in the rate constant obtained using CVTST.     

Excitation mechanisms in CW He-Hg lasers

The collision processes responsible for populating and de-populating upper and lower levels of the cw He-Hg ion laser are investigated using flowing afterglow techniques. It is shown that the superior performance of the laser at 6150 Å compared to that at 7945 Å is not due to a difference in excitation mechanism — both are excited by charge transfer from He⁺ — but instead reflects a greater effectiveness of second kind collisions of electrons in depopulating the 7p²P_{$\text{1}\text{2}$} upper level of the 7945 Å transition. The charge transfer, excitation rate constants for several Hg II levels are compared, and values for the rate constant for the electron collision de-excitation process are deduced.     

The Near-Infrared YΣ-XΠ Transition of CuSe

The near-infrared Y²Σ⁺-X²Π transition of the diatomic molecule CuSe was observed for the first time. A King-type carbon tube furnace was used to produce the gas phase of the CuSe molecules. The Fourier transform spectrometer associated with the National Solar Observatory, Kitt Peak, Arizona was used to record the molecular emission spectrum in the region 9850-12 400 cm⁻¹. A vibronic analysis and comparisons of the spin-orbit constant and the ²Σ⁺ transition energy to those for related isovalent molecules are presented.     

The optimization of potential energy surface parameters for the CsCl + RbI system with the use of linear regression analysis

The influence of interaction potential parameters of likely charged ions on cross sections of various channels of a reaction of a pair of diatomic molecules with ionic bonds was studied in terms of quasi-classical trajectory simulation with the use of linear mean-square regressions. In the regression approach, the dependence of the cross section of a given reaction channel on potential parameters at each fixed collision energy is approximated by a linear function. We determined the region of softness parameters of the Cs⁺-Rb⁺ and Cl⁻-I⁻ interaction potentials. This region was optimum for the reproduction of experimental excitation functions of atomic and complex positive ions for the CsCl + RbI → products reaction.     

Lie Algebraic Approach to Energy Transfer for Collinear Collision of Two Anharmonic Diatomic Molecules

An anharmonic oscillator algebra model is used to study the collinear collisions of two diatomic molecules. The transition probability for vibration-vibration energy transfer is presented. For an application of the method, we talk about the collision of N2＋CO, N2＋O2, and N2＋N2. Through long time averaging, the transition probability changes to the function of total energy of the system. Comparing the results with the quantum results, we can see that the dynamical Lie algebraic method is useful for describing the anharmonie diatomic molecular collision.     

H2SiCl2 中 SiH 伸缩振动的泛频光谱

在2000 ～ 9000 波数 、 12000 ～12900 波数的光谱区间记录了室温下H2SiCl2气体分子的振动泛频光谱，所用的仪器分别是高分辨傅立叶变换光谱仪和高灵敏激光腔内吸收光谱仪。用局域模模型和包含达林－丹尼生共振的简正模模型，归属了SiH伸缩振动的基频和泛频，振动量子数的改变△VSiH=1, 2, 3, 4 and 6。通过对实验能级的非线性拟合，得到SiH伸缩振动的谐振频率ωm、非谐性常数χm、键间耦合系数λ、莫尔斯振子参数 De、α 和相互作用力常数 。实验发现，随着振动能量的增加，振动簇（manifold，两个SiH键的伸缩振动量子数m+n=常数 ）中能量最低的两个能级的间距逐渐减小。当△VSiH≥4时，在实验误差范围内这两个最低的振动态能级简并。这种简并的能级结构类似双原子莫尔斯振子，符合Birge-Sponer 关系。双原子莫尔斯振子直接描述了H2SiCl2分子中SiH 的高泛频伸缩振动，表明在高振动情况下振动能量已经集中到单个SiH键上。     

双光子共振非简并四波混频测量Ba原子里德伯态的碰撞展宽和频移

采用双光子共振非简并四波混频测量了Ar缓冲气压引起的Ba原子里德伯6snd ¹D₂谱线系的碰撞展宽和频移, 计算了n=16---33的碰撞展宽截面和频移截面. 本方法是一种纯光学的测量技术, 当采用窄带激光器时可以获得里德伯态的消多普勒光谱. 与传统实验方法测量到的里德伯态纵向弛豫的碰撞展宽不同, 本方法可以研究碰撞引起的两能态间横向弛豫的展宽.     

Fine structure and centrifugal distortion in the electronic and microwave spectra of O2 and SO

The fine structure theory of ³Σ states in diatomic molecules is re-examined with particular emphasis on centrifugal distortion in the triplet splitting parameters. The theoretical results are compared with optical and microwave data for the ³Σ ground states of O₂ and SO. Excellent agreement is found between theoretical predictions and experimental results concerning the centrifugal distortion in the spin-spin splitting for both O₂ and SO. However, in contrast to ab initio calculations this agreement indicates that the second-order contribution to the spin-spin splitting is of minor importance. The theoretical value of the centrifugal distortion in the spin-rotation coupling constant is about twice the experimental one for O₂. It is pointed out that a slight transition towards coupling case (c) yields a reasonable explanation for this discrepancy.     

Reactive scattering of a supersonic oxygen atom beam O+ICl

Reactive scattering of O atoms with ICl molecules has been studied at an initial translational energy E = 40 kJ mol^-1 using a supersonic beam of O atoms seeded in He and at E = 15 kJ mol^-1 using O atoms seeded in Ne. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. Full contour maps of the differential reaction cross-section have been obtained which show peaking almost equally in the forward and backward directions at both initial translational energies. The product translational energy distributions are consistent with a long-lived O-I-Cl collision complex dissociating via a loose transition state. The stability of the O-I-Cl complex is attributed to the low electronegativity of the central I atom compared with the peripheral atoms. This electronegativity ordering rule also determines the stability of the intermediates in the other reactions of oxygen atoms with halogen molecules. The mild peaking of the product angular distributions for O + ICl and IBr indicates that collision complexes have quite modest collision angular momenta L ～ 40 ? corresponding to impact parameters b ～ 1·4 Å and that the angular momentum of the OI molecule in the loose transition state may be approximately half the product orbital angular momentum.     

A theoretical study of energy transfer in the quenching of O(1 D 2) by CO(1Σ+)

Energy transfer processes occurring during the collisional quenching of O(¹ D) by CO(¹Σ⁺) are studied using a classical collision complex model together with potentials previously derived for the C(³ P) + O₂(³Σ _g ^-) reaction. Room temperature quenching rate constants, electronic-vibrational transfer efficiencies and product vibrational state distributions are in good agreement with experiment. The calculated and experimental temperature dependences of the electronic-vibrational transfer efficiencies and vibrational populations, however, disagree. The effect of using vibrationally excited CO as a quenching partner is studied and shown to result in a lowering of the quenching rate constant by a factor of 4 at room temperature. Enhancement of initial translational energy by the equivalent of a vibrational quantum of energy leads to an even larger decrease in the rate constant. This difference between vibrational and translational energy enhancement is interpreted in terms of an increased centrifugal barrier in the latter case.     

Conversion efficiency of ultracold fermionic atoms to bosonic molecules via Feshbach resonance sweep experiments

We explain why the experimental efficiency observed in the conversion of ultracold Fermi gases of 40K and 6Li atoms into diatomic Bose gases is limited to 0.5 when the Feshbach resonance sweep rate is sufficiently slow to pass adiabatically through the Landau-Zener transition but faster than "the collision rate" in the gas, and increases beyond 0.5 when it is slower. The 0.5 efficiency limit is due to the preparation of a statistical mixture of two spin states, required to enable s-wave scattering. By constructing the many-body state of the system we show that this preparation yields a mixture of even and odd parity pair states, where only even parity can produce molecules. The odd parity spin-symmetric states must decorrelate before the constituent atoms can further Feshbach scatter, thereby increasing the conversion efficiency; "the collision rate" is the pair decorrelation rate.     

The fluctuation enhanced conductivity in amorphous superconductors

Considering the effective phonon density of states obtained by tunnel spectroscopic measurements, we conclude that in amorphous metals such as Bi, Ga, and Pb, the electron-phonon collision rate becomes as large as 10¹²/sec at the transition temperature. This is attributed to the collision drag effect which couples low frequency transverse phonons to the electrons. It is shown that such a large collision rate suppresses the Maki contribution to the fluctuation enhanced conductivity.     

Vibrational and rotational excitation effects of the N(2D) + D2(X1Σg +) → ND(X3Σ+) + D(2S) reaction

The effects of the rovibrational excitation of reactants in the N(²D) + D₂(X¹Σ_g⁺) → ND(X³Σ⁺) + D(²S) reaction are calculated in a collision energy range from the threshold to 1.0 eV using the time-dependent wave packet approach and a second-order split operator. The reaction probability, integral cross-section, differential cross-section and rate constant of the title reaction are calculated. The integral cross-section and rate constant of the initial states v = 0, j = 0, 1, are in good agreement with experimental data available in the literature. The rotational excitation of the D₂ molecule has little effect on reaction probability, integral cross-section and the rate constant, but it increased the sideways and forward scattering signals. The vibrational excitation of the D₂ molecule reduced the threshold and broke up the forward–backward symmetry of the differential cross-section; it also increased the forward scattering signals. This may be because the vibrational excitation of the D₂ molecule reduced the lifetime of the intermediate complex.     

A New Relation Free From Electronegativity For Vibrational Constant Of Diatomic Molecules

Most of the previous relations^1–3 for the calculation of vibrational constant of diatomic molecules are electronegativity dependent. Electronegativity (X) is a complex quantity containing an atomic term depending on the charge and hybridization of the atom, and a molecular term depending on the length and the nature of the bonds in the molecule and as such it is not as precise as the bond length r_e or the reduced mass μ of the molecule. Thus the formule dependent on the electronegativity are expected to yield divergent results. Though there is a relation given by Varshni and Guggenheimer⁴ which is free from electronegativity but the drawback is that it depends on too many quantities and also contains two empirical constants. Therefore it was thought to propose a new relation free from electronegativity, containing a single constant A, depending only on r_e and μ.     

Frequency measurements in the b <Superscript>3</Superscript>Π(0<Subscript>u</Subscript><Superscript>+</Superscript>) - X <Superscript>1</Superscript>Σ<Subscript>g</Subscript><Superscript>+</Superscript> system of K<Subscript>2</Subscript>

Absolute transition frequencies of the b ³Π(0_u ⁺) - X ¹Σ_g ⁺ system of K₂ were measured in a molecular beam with Lamb dip absorption spectroscopy applying a frequency comb from a femtosecond pulsed laser. Both, K atoms and K₂ molecules are present in the beam and are expected to interact by collisions. The atoms can be deflected optically out of the beam, and thus the collision rate between K atoms and K₂ molecules is changed by about an order of magnitude. The molecular transition frequencies for low collisional rate are compared with those for high one. Limits for the collisional frequency shift within the beam are determined.     

Ar-HCl转动跃迁光谱线压力加宽截面的理论计算

本文利用量子力学的Infinite Order Sudden Approximation近似方法和Ar-HCl H6(2)相互作用解析势模型,计算了HCl分子转动跃迁谱线被Ar展宽的压力加宽截面（相对能量范围30cm^-1—1000^-1)和平均弛豫截面（系统温度125K,175K,300K）.通过与密耦合方法（CC）计算值及实验值的比较,发现IOSA近似方法对转动能级较为稀疏的分子的j=0←j=1转动路迁谱线仍然可给出较好的计算结果,但要用于转动激发态跃迁谱线的计 关键词：     

Transition rates between fine structure components in he and He-like ions during collisions with protons

The transition rates between fine structure components of triplet levels with n = 2, 3 in He and He-like ions during collision with protons are considered. The problem specificity is the existence of a virtual level connected to multiplet components by dipole-allowed transitions. As a result, a broad peak appears in the dependence of the transition rate on the plasma temperature. Calculations for transitions were performed within the 2³P, 3³P, and 3³D terms in He, C⁴⁺ and Fe²⁴⁺.     

Bremsstrahlung in heavy-ion molecular resonances

The bremsstrahlung cross section for the quadrupole photon emission in a heavy-ion collision is formulated on the basis of the coupled-channel method. For the branching ratio of the radiative decay width to the total width for the transition between the structures at 25.6 MeV and 19.3 MeV in the ¹²C + ¹²C collision, we predict (3–7) × 10^?7, which is roughly comparable with existing measurements. The radiation from the mutual 2⁺ excitation channel is found to yield 70% of the total branching ratio.     

CNDO/SP calculation of g-tensors of free radicals

Exact expressions are derived for the rate of stimulated emission and the conditions for population inversion in a diatomic bound-continuum transition. The resultant formulae resemble those of a simple, homogeneously broadened, discrete transition with the Lorentzian lineshape replaced by a continuum lineshape, g ^C(hv = E_v ′ - ε″), which is approximately equal to the square of the overlap between the initial, emitting, vibrational level v′ and the final, energy-normalized continuum state ε″, i.e. g ^C ≈ v′|ε″>². Using the ‘reflection method’, which is most applicable to a strongly repulsive final state, equations are obtained which allow simple, but accurate, estimation of the pertinent parameters which influence lasing action. Some general conclusions are extracted, and specific results are presented for the stimulated vacuum ultra-violet emission in high pressure Xe.