The rotational levels of the ground vibrational state of formaldehyde

A variational procedure for rovibrational energy levels and wavefunctions of centrally connected tetra-atomic molecules is extended to include high rotational states, and in particular, J ? 10 levels for the vibrational ground state of formaldehyde. It is very important to do this because it has made possible the calculation of the usual rotational spectroscopic constants which correspond to the forcefield and geometry. A direct comparison with the ‘observed’ spectroscopic constants is therefore possible. The geometry and forcefield are refined against 65 J = 0 levels of H₂CO, 6 J = 0 levels of D₂CO, 42 J = 1, 70 J = 2 and 98 J = 3 levels of the ground and fundamentals of H₂CO and D₂CO, using an iterative scheme. The mean absolute error of the J = 0 levels is 1·10 cm^?1 and that for J ≠ 0 is 0·005 cm^?1, and the predicted geometry is CH = 1·10064 Å, CO = 1·20296 Å and HCO = 121·648°. Finally, the rotational constants A, B, and C for the ground state are 281956, 38846 and 34003 MHz, compared with the observed values 281971, 38836, and 34002 MHz. The centrifugal distortion constants Δ_J , Δ_JK , Δ_K and δ_J , are 77, 1275, 18113 and 11 kHz compared with 75, 1291, 19422 and 10 kHz. These results underline the accuracy of the new quartic forcefield.     

Submillimeter spectrum and spectroscopic constants of the arsine molecule in the ground vibrational state

The submillimeter spectrum of the arsine molecule, AsH₃, of both the allowed R-branch transitions (J + 1 ← J, J = 0, 1, 2, 3) and forbidden transitions of the Q branches, |K| = 4 ← 7, 5 ← 8, 6 ← 9, is investigated in the frequency range from 220 to 900 GHz. Weak absorption lines were observed by using the spectrometer RAD with sensitivity increased by a nontunable cavity cell. On the basis of the results obtained and microwave data available in the literature the rotational spectrum of the arsine molecule in the ground state is analyzed.     

Rotational spectrum and spectroscopic constants of the phosphine molecule in the ground vibrational state

A comprehensive investigation of both the allowed and the forbidden rotational spectra of the phosphine molecule, PH₃, in the ground vibrational state is described. The new experimental microwave investigation covers the frequency region from 300 to 1070 GHz.     

Calculations of the polarizability and hyperpolarizability of the NaH molecule including vibrational corrections

In this work we present results for the dipole moment, polarizability and first hyperpolarizability of the NaH molecule obtained through the many-body perturbation-theory, coupled cluster and quadratic configuration interaction methods, including vibrational corrections. It is shown that the nuclear relaxation contribution is of fundamental importance for both polarizability and first hyperpolarizability of this system. Besides, inclusion of electron correlation effects changes appreciably the size of this contribution. In addition, our results show that the curvature contribution does not alter significantly the values obtained for the polarizability.     

Formation of ground-state vibrational wave packets in intense ultrashort laser pulses

The formation of coherent vibrational wave packets in the electronic ground state of neutral molecules in intense ultrashort laser pulses and their subsequent detection by means of recently developed pump-probe experiments are discussed. The wave packet formation is due to the pronounced dependence of the strong-field ionization rate on the internuclear distance. This leads to a deformation of the initial wave function due to an internuclear-distance dependent depletion. The phenomenon is demonstrated with a time-dependent wave packet study for molecular hydrogen.     

Improved potential energy curve and vibrational energies for the electronic ground state of the hydrogen molecule

The potential energy curve for the electronic ground state of the hydrogen molecule has been recomputed for intermediate and large internuclear separations. for 2.4 ≤ R ≤ 8.0a.u. the previous potential energy curve has been improved. The largest improvement amounts to 5.5 cm^?1, and was obtained in the vicinity of R = 4.4a.u.. Using the new potential energy curve, and the adiabatic and relativistic corrections, the vibrational and rotational energy levels have been calculated for H₂, HD, and D₂. The deviations of the calculated energy levels G(v) of H₂ and D₂ from the observed values follow very closely the nonadiabatic corrections resulting from the Van Vleck formula.     

Millimeter-wave spectrum of DCCCHO in the ground vibrational state

About 140 a- and b-type millimeter-wave transitions of propynal-d₁, DCCCHO, were measured in the ground vibrational state. The accurate rotational and centrifugal distortion constants were determined from the observed frequencies including the previous microwave measurements. Seven microwave transitions observed by infrared-microwave double resonance were also included in the analysis. The determined constants are A = 66778.016(12), B = 4463.8489(7), C = 4177.7950(7), Δ_J = 0.0015919(5), Δ_JK = −0.139214(13), Δ_K = 9.4328(18), δ_J = 0.0002885(4), δ_K = 0.03069(4), H_JK = −0.817(13) × 10⁻⁶, H_KJ = −9.62(4) × 10⁻⁶, H_K = 0.00255(8), h_J = 0.0047(3) × 10⁻⁶, in MHz.     

Remote sensing of the atmosphere using ultrashort laser pulses

Theoretical and experimental studies were performed on the propagation of ultrashort optical terawatt pulses through the atmosphere. Propagation simulations of intense sub-picosecond pulses show that non-linear processes, such as white light generation, can be initiated at a chosen distance by selecting an appropriate group velocity dispersion. With this technique, a white light continuum was generated in the atmosphere whose spectral distribution was characterised in the visible and near infra-red. Applications of this novel light source for atmospheric remote sensing were investigated, combining lidar and time-resolved broadband absorption spectroscopy techniques. Measurements were performed on the oxygen molecule and water vapour. A comparison between the experimental results and the tabulated spectroscopic data led to an excellent correlation with measurements made on water vapour whereas observations on the oxygen showed discrepancy. This study demonstrates that the remote generation of a white light source represents a new way to access the range-resolved multi-trace gas analysis in the atmosphere. Received: 8 December 1999 / Revised version: 18 May 2000 / Published online: 16 August 2000     

Control of electron excitation and localization in the dissociation of H2(+) and its isotopes using two sequential ultrashort laser pulses

We study the control of dissociation of the hydrogen molecular ion and its isotopes exposed to two ultrashort laser pulses by solving the time-dependent Schr?dinger equation. While the first ultraviolet pulse is used to excite the electron wave packet on the dissociative 2psigma{u} state, a second time-delayed near-infrared pulse steers the electron between the nuclei. Our results show that by adjusting the time delay between the pulses and the carrier-envelope phase of the near-infrared pulse, a high degree of control over the electron localization on one of the dissociating nuclei can be achieved (in about 85% of all fragmentation events). The results demonstrate that current (sub-)femtosecond technology can provide a control over both electron excitation and localization in the fragmentation of molecules.     

Submillimeter rotational spectrum of formamide in the ground vibrational state

Radio Astronomy Institute, Academy of Sciences of the Ukrainian SSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 2, pp. 213–216, February, 1991.     

Determination of relaxation times of ground electronic state vibrational levels of mixed molecular crystals

The stimulated emission spectra of mixed molecular crystals were investigated with the Nd glass lasser third harmonic excitation at 4.2 K. Napthalene crystals doped with β-naphthyl-n-biphenylyl ethylene and dibenzyl doped with naphthacene in various concentrations were studied. Relaxation times of the ground state vibrational levels in mixed molecules were obtained by use of the dependence of stimulated emission intensity upon excitation energy for naphthacene in dibenzyl τ₁ of the vibrational level at 317 cm^-1 was ～ 3 × 10^-9 s; for β-naphthyl-n-biphenylyl ethylene in naphthalene τ₁ of the 1629 cm^-1 vibrational level was ～ 10^-10 s.     

一种确定双原子分子基电子态的新方法

针对某些双原子分子基电子态与激发态势能曲线存在相交,从而引起利用从头计算确定分子基电子态时因初始输入不同而确定出的基态不同的情况,提出了一种将势能曲线计算和优化计算相结合确定基电子态的方法,并运用它确定B+2分子的基电子态.解释了文献中对于它的基电子态的计算出现不同结果的原因.     

Nonadiabatic effects in the ground state of the hydrogen molecule

A sum-over-states procedure is used in the ab initio evaluation of the matrix elements needed for a nonadiabatic treatment of the ground electronic state of H₂. Bunker's (J. Mol. Spectrosc.42, 478 (1972)) semiempirical value for the nonadiabatic parameter l₁ = 0.130 ± 0.006 is in agreement with the present calculation, which therefore supports the interpretation of the difference between theoretical adiabatic and experimental vibrational energies as being due to nonadiabatic effects. The same techniques are used to evaluate the expectation value of $\text{?}{}^2\text{?R}{}^2$ in the H₂ ground electronic state. Finally, it is pointed out that an average energy denominator used in several recent treatments of nonadiabatic effects in H₂ is in error by roughly a factor of two. The correct average energy denominator reflects that the sums have large contributions from states in the electronic continuum.     

Quantum-classical simulation of the photoisomerization during the transformation of ultrashort light pulses by a molecule

The dynamics of photoisomerization of a model molecule during its transformation of ultrashort (with a duration much shorter than the lifetime of the resonant excited electronic state) light pulses is simulated numerically. The two-level electronic subsystem of the molecule is described using the quantum theory, while the nuclear subsystem (taking into account the two isomeric states of the molecule) and the radiation field are described using the classical theory. The ranges of the carrier frequency, the peak intensity, and the durations of nπ sinusoidal pulses (n = 1–10) irradiation with which results in the photoisomerization of molecules of the type under study (for example, cyanine dyes) are determined from the analysis of solutions to self-consistent equations that describe the motion of the “isomerization oscillator” and the time evolution of the population amplitude of the resonant electronic state of the molecule. Each of these non-overlapping ranges corresponds to a particular value of n. Bifurcation values of the above parameters of the light pulse are boundaries of these ranges.     

Determination of dispersion characteristics in anisotropic materials using ultrashort pulses

2 crystal. This method, based on group velocity measurement, allows the determination of the principal axes, the indices, the group velocities and the group velocity dispersion (GVD). Received: 11 February 1997/Revised version: 23 May 1997     

超短脉冲激光在DBASVP分子中传播时的双光子面积演化和光限幅效应

以一维不对称π共轭分子体系（DBASVP分子）为介质,在双光子共振条件下,从双光子面积定理和严格数值求解Maxwell-Bloch方程两方面出发,分别研究超短脉冲激光在该有机分子介质中的传播过程,从而探讨双光子面积的演化规律,并分析双光子面积定理的适用性.提出了一种数值模拟分子介质光限幅特性的理论方法.分子的电子结构和电偶极矩是基于密度泛函理论利用从头计算方法得到的.研究结果表明,基于慢变幅和慢变相近似以及单模场条件下的双光子面积定理不能很好地描述超短脉冲的双光子面积在该分子介质中的演化规律.基于双光子吸收的分子光限幅特性与分子介质的厚度有关. 关键词： 双光子吸收 光限幅效应 双光子面积定理 超短脉冲激光