Pressure-induced broadening of hyperfine components of rotational transitions of methyl cyanide molecule

The broadening of hyperfine components of rotational transitions of the methyl cyanide molecule is considered in terms of the collision approximation based on the theory previously developed by the author. The role played by possible collisional interference processes is examined. Relaxation parameters are calculated, and broadening coefficients are compared to the experimental data.     

A tunable laser at λ=3.39 μm with line width of 7 Hz used in investigating a hyperfine structure of theF 2 (2) line of methane

A laser spectrometer is described which was used in exploring resonance shapes of about 1000 Hz width in methane in the region of low absorption of about 10⁻⁶ cm⁻¹. We report on first measurements of relative intensities of hyperfine components of theF ₂ ⁽²⁾ line in methane, on direct observations of line splitting due to a recoil effect and of a non-linear dependence of collisional broadening of resonances in the transit region, and on observation of an anomalous Zeeman effect in hyperfine components in a longitudinal magnetic field. The results of this work were summarized by one of the authors (V.C.) at the 2nd Symposium on Frequency Standards and Metrology (Boulder, Colo., USA, July 1976) and at lectures in the School Enrico Fermi (Varenna, Italy, July 1976).     

H(2)-Broadening Coefficients in the nu(4) Band of NH(3)

H(2)-broadening coefficients have been measured for 66 rovibrational lines of NH(3) at room temperature in the (P)P and (R)P branches of the nu(4) band in the range 1470-1600 cm(-1), using a high-resolution Fourier transform spectrometer. The collisional widths are obtained by fitting Voigt profiles to the measured shapes of the lines. The broadening coefficients are found to decrease on the whole as J increases and they increase with K for a given J value. The results are compared with those calculated from a semiclassical model in which the inversion vibration of NH(3) and collision-induced transitions with DeltaK = 0 and DeltaK = +/- 3 are taken into account. The intermolecular potential used includes electrostatic, induction, and dispersion energy contributions. The calculations performed by considering only DeltaK = 0 transitions provide significantly lower broadenings but with a satisfactory J and K dependence. The same trends are obtained for the broadening coefficients in inversion-rotation transitions and in the Q branch of the nu(1) parallel band of NH(3). Copyright 2001 Academic Press.     

Pressure induced frequency shifts in the atomic iodine laser

The frequency of oscillation of an iodine photodissociation laser has been measured for argon buffer gas pressures up to 7 atmospheres. The variation in frequency of the 1.315 μm transition can be explained solely by the overlapping of the hyperfine split transitions at high pressures, and no evidence is obtained for a collisional frequency shift. A pressure broadening parameter of 4.5 MHz/torr for argon-iodine collisions is deduced from the observed frequency shifts.     

Quantitative analysis of dinuclear manganese(II) EPR spectra

A quantitative method for the analysis of EPR spectra from dinuclear Mn(II) complexes is presented. The complex [(Me(3)TACN)(2)Mn(II)(2)(mu-OAc)(3)]BPh(4) (1) (Me(3)TACN=N, N('),N(")-trimethyl-1,4,7-triazacyclononane; OAc=acetate(1-); BPh(4)=tetraphenylborate(1-)) was studied with EPR spectroscopy at X- and Q-band frequencies, for both perpendicular and parallel polarizations of the microwave field, and with variable temperature (2-50K). Complex 1 is an antiferromagnetically coupled dimer which shows signals from all excited spin manifolds, S=1 to 5. The spectra were simulated with diagonalization of the full spin Hamiltonian which includes the Zeeman and zero-field splittings of the individual manganese sites within the dimer, the exchange and dipolar coupling between the two manganese sites of the dimer, and the nuclear hyperfine coupling for each manganese ion. All possible transitions for all spin manifolds were simulated, with the intensities determined from the calculated probability of each transition. In addition, the non-uniform broadening of all resonances was quantitatively predicted using a lineshape model based on D- and r-strain. As the temperature is increased from 2K, an 11-line hyperfine pattern characteristic of dinuclear Mn(II) is first observed from the S=3 manifold. D- and r-strain are the dominate broadening effects that determine where the hyperfine pattern will be resolved. A single unique parameter set was found to simulate all spectra arising for all temperatures, microwave frequencies, and microwave modes. The simulations are quantitative, allowing for the first time the determination of species concentrations directly from EPR spectra. Thus, this work describes the first method for the quantitative characterization of EPR spectra of dinuclear manganese centers in model complexes and proteins. The exchange coupling parameter J for complex 1 was determined (J=-1.5+/-0.3 cm(-1); H(ex)=-2JS(1).S(2)) and found to be in agreement with a previous determination from magnetization. The phenomenon of exchange striction was found to be insignificant for 1.     

Pressure broadening by argon in the hyperfine resolved P(10) and P(70) (17,1) transitions of I2 XΣ(0g)→BΠ(0u) using sub-Doppler laser saturation spectroscopy

The dependence of pressure broadening upon hyperfine component in the P(10) and P(70) lines of the (17,1) band of the I₂ X¹Σ(0_g⁺)→B³Π(0_u⁺) has been studied using laser saturation spectroscopy. By limiting absorption to the zero velocity group, Doppler broadening is removed, lineshapes with widths (FWHM) <9 MHz are detectable, and collision-induced broadening is measured at pressures of 0.2-1.2 Torr. The rates for broadening by argon are 8.3±0.3 and 10.7±0.4 MHz/Torr for the P(70) and P(10) lines, respectively. No significant variation in broadening rates is observed for the 15 hyperfine components of these even rotational lines. The effects of velocity cross-relaxation introduce a broad baseline into the spectra, which is strongly dependent on rotational state, pressure, and laser modulation frequency. The observed broadening rates correlate well with prior measurements and the polarizability of the collision partner.     

Cs-He混合蒸气中的辐射陷获效应和6P3／2能级有效辐射率的测量

测量了Cs-He混合蒸气中Cs(6P3/2)共振能级的有效辐射率,圆柱形样品池充入金属Cs和气压PHe为0~500Pa的He,样品池温度控制在330~370K之间,在池中产生1012~1013cm-3的Cs原子密度,使用单模半导体激光器(泵浦激光)将Cs原子激发至6P3/2态,另一调谐到6P3/2→8S1/2的单模激光束(检测激光)与泵浦束反平行通过样品池,并在池的直径方向平行移动,通过对检测激光束的吸收测定了激发态原子密度及其空间分布。由于辐射陷获存在,有效辐射率是自然辐射率与透射因子(发射的光子在探测区域内没有被吸收的平均概率,它与吸收截面及激发态原子密度和空间分布有关)的乘积。由6P3/2原子密度及其空间分布结合6P3/2←6S1/2跃迁线的碰撞增宽计算了透射因子,从而得到了不同He气压下,CsD2线的有效辐射率。从6P3/26→S1/2跃迁线强度I852的测量,得到的不同He气压下有效辐射率的比值与理论计算得到的比值相符。     

Diode-Laser Measurements of N(2)-Broadening Coefficients in the nu(7) Band of C(2)H(4)

N(2)-broadening coefficients have been measured for 35 lines of C(2)H(4) in the nu(7) fundamental transition, using a tunable diode-laser spectrometer. These lines with 3 相似文献   

Narrowing broadening and shifting parameters for R(2) and P(14) lines in the HCl fundamental band perturbed by N2 and rare gases from tunable diode laser spectroscopy

High resolution measurements of room temperature absorption with a controlled tunable diode laser (TDL) spectrometer have been made for R(2) and P(14) lines in the HCl fundamental band perturbed by N₂, Xe, Ar and He at pressures lower than one atmosphere. Pressure broadening, shift and collisional narrowing parameters have been extracted by least-squares fitting of several collisional profiles to the spectra. Asymmetries are observed for P(14) broadened by Xe at the lowest pressures and attributed to correlations between velocity- and phase-changing collisions.     

Effects of collisional interference of lines in the spectra of symmetric top molecules: III. Broadening of rotational transitions with a hyperfine structure

The peculiarities of the broadening of rotational transitions of molecules in the case where the spectrum exhibits a hyperfine structure caused by the nuclear quadrupole interaction are considered. The relaxation parameters of the components of a number of hyperfine multiplets of CH₃I molecules are calculated taking into account self-broadening, and calculations are compared with experiment.     

Ligand exchange reactions between copper(II)- and nickel(II)-chelates of different sulphur- and selenium-containing ligands

A single-crystal E.S.R. and multi-nuclear ENDOR study of the mixed ligand complex tetra-n-butylammonium(maleonitriledithiolato)(monoethyldithiophosphato)cuprate(II), diamagnetically diluted by the corresponding Ni(II) complex, and the crystal structure of the host complex are reported. n-Bu₄N[Ni(mnt)(HEtdtp)].0·7 acetone is triclinic, space group P1, Z = 2 with a = 9·029(2), b = 13·432(4), c = 17·246(5) Å, α = 108·9(1), β = 90·2(1) and γ = 109·4(1)°. The spin-hamiltonian parameters are calculated from the results of an extended Hückel molecular orbital calculation. The experimental g-tensor and the copper and the four sulphur hyperfine coupling tensors are reporduced well. The almost isotropic and unexpectedly large coupling of the phosphorous atom is negative, which can be understood qualitatively from a spin polarization mechanism.

The hyperfine coupling tensors of eight protons, three of the acetone molecule, four of the tetra-n-butylammonium cation and one intramolecular one, could be determined. The E.S.R. linewidths are unusually small for Cu complexes. Unresolved proton hyperfine interactions are found to give the largest contribution.     

Improvement of spectral resolution by using the excitation dependence of dipole–dipole interaction in a dense atomic gas

We have studied the selective reflection from the interface between a dense rubidium (Rb) atomic vapor and a transparent dielectric. A remarkable narrowing of the spectrum, which can be used to improve the resolution of spectroscopy of dense media, has been demonstrated. This narrowing results from the reduction of the dipole–dipole interaction between atoms when the Rb vapor is excited by a strong pump laser. By using this technique, we have resolved the hyperfine structure of the Rb D₂ line, which is hidden by collisional broadening. PACS 32.70.Jz; 42.50.Ct; 34.80.Dp     

Nuclear Quadrupole Tensors for (35)Cl and (37)Cl in cis-1-chloro-2-fluoroethylene Obtained by Detection of Perturbation-Allowed DeltaJ = 2 and DeltaJ = 3 Transitions

The nuclear quadrupole hyperfine structure in rotational transitions of cis-1-chloro-2-fluoroethylene was measured for both (35)Cl and (37)Cl containing isotopomers in the millimeter-wave region. Near degeneracies of the 9(3,7) and 10(2,9) levels of (35)ClHC&dbond;CFH and of the 19(9,10/11) and 17(10,7/8) levels of (37)ClHC&dbond;CFH cause strong perturbations of the hyperfine patterns and give rise to perturbation-allowed DeltaJ = 2 and DeltaJ = 3 transitions. Lamb-dip measurements of such perturbed hyperfine patterns and of forbidden DeltaJ = +2 and perturbation-enhanced DeltaJ = 0 transitions of (35)ClHC&dbond;CFH provided an accurate determination of chi(ab), the off-diagonal element of the inertial nuclear quadrupole tensor. For (37)ClHC&dbond;CFH, chi(ab) was determined for the first time thanks to the observation of perturbed hyperfine patterns and of forbidden DeltaJ = +3 and DeltaJ = -2 transitions. Additional measurements of hyperfine structures led to improved values for the diagonal elements of the chi tensor of both (35)Cl and (37)Cl. Moreover, the complete inertial nuclear quadrupole tensor was evaluated from the field gradient at the chlorine nucleus computed by using the Multi-Configuration Self-Consistent Field (MCSCF) approach and employing basis sets of triple-zeta quality: very good agreement with the experiment was obtained. Copyright 2000 Academic Press.     

Measurements and analysis of collisional line-mixing within nuclear hyperfine components of helium broadened HI lines

The absorption by the R (0) and R (1) lines of the fundamental band of HI broadened by He have been measured in the 0-500 mbar pressure range using a tunable difference frequency generation laser spectrometer. The observed transmissions have been fitted and analyzed with a line-coupling model based on the infinite order sudden approximation. It is demonstrated that the three hyperfine components of the R (0) manifold have identical widths and are not coupled by collisions. On the contrary, the profile of the R (1) manifold cannot be modeled without accounting for both line-mixing and for the fact that the nine hyperfine components have different broadening parameters. This is, to our knowledge, the first demonstration of line coupling within hyperfine components.     

Broadening and collisional interference of lines in the IR spectra of ammonia. Theory

The general theory of relaxation spectral shape parameters in the impact approximation (M. R. Cherkasov, J. Quant. Spectrosc. Radiat. Transfer 141, 73 (2014)) is adapted to the case of line broadening of infrared spectra of ammonia. Specific features of line broadening of parallel and perpendicular bands are discussed. It is shown that in both cases the spectrum consists of independently broadened singlets and doublets; however, the components of doublets can be affected by collisional interference. The paper is the first part of a cycle of studies devoted to the problems of spectral line broadening of ammonia.     

水汽分子对CO_2谱线加宽的影响

报道了以高分辨力连续可调谐中红外差频激光为探测光源,结合可调长光程怀特池,利用直接吸收的方法探测了CO2的10011←10002带R支以及部分P支在室温下的水汽加宽吸收光谱。在2422cm-1到2457cm-1范围内共有26条吸收谱线被探测到,采用Voigt线型对吸收谱线进行拟合,得到了CO2光谱的水汽加宽系数,结果显示CO2的水汽加宽系数平均比干燥空气的加宽系数大52%。利用实验测得的CO2的水汽加宽系数与HITRAN04数据库中CO2谱线的线位置、线强和干燥的空气加宽系数进行比较,分析了在实际大气中(海平面,10km光程)不存在水汽和存在水汽(含有2.0kPa水汽)时该波段CO2的大气透过率,结果表明潮湿空气与干燥空气之间的最大透过率差约为0.5‰。     

Collisional effects on the HFS transitions of antiprotonic helium

Collisions of metastable antiprotonic helium with ordinary He atoms can induce transitions between hyperfine structure (HFS) sublevels and thus relaxation of the populations as well as shift and broadening of M1 microwave spectral lines. Previously we have considered these effects, using quantum close-coupling method for the collisions and the model interatomic interaction involving tensor term (Korenman and Yudin, J Phys B At Mol Opt Phys 39:1473–1484, 2006). In this paper we extend the consideration in two lines: (i) collisional transition rates, shifts and broadenings of M1-lines are considered in relation to the strength of the tensor interaction; (ii) time evolution of the density matrix of HFS states is considered using the generalized master equation with the calculated elementary characteristics. A good agreement with the recent experimental data on the time dependence of optimum signal-to-noise ratio and of linewidth is obtained using the strength of tensor interactions as a free parameter.     

Magnetic hyperfine fields of vacancy-associated119Sn in ion-implanted nickel

Magnetic hyperfine fields of¹¹⁹Sn impurity defects in nickel have been investigated by Mössbauer emission spectroscopy. Radioactive¹¹⁹Xe isotopes were implanted, annealing was performed after¹¹⁹Xe had decayed to¹¹⁹Sb. At least five different components with well-defined magnetic hyperfine fields, isomer shifts and Debye temperatures are identified in the rather complex spectra. One of these (B=2T) is known to be due to substitutional Sn. The hyperfine fields of the other components are pronouncedly larger (B=9T, B=15T, and B=17T, respectively, for single crystals). These defects are proposed to be Sn-multivacancy defects.     

Experimental and theoretical studies of room-temperature sub-millimetre CH3 35Cl line shapes broadened by H2

Hydrogen-broadening coefficients of methyl chloride rotational lines J?=?6?→?7, 10?→?11, 17?→?18, 22?→?23 and 31?→?32 at 296?K are measured as functions of the quantum number K using a sensitive frequency-modulation technique. As expected for this light perturber, the observed line shapes are well described by Voigt profile model. A clear dependence of the collisional broadening on K is observed for most transitions. From a detailed study of the K-components of the transition J?=?6?→?7 situated at 186?GHz no variation of the broadening of the hyperfine components related to ³⁵Cl quadrupole is stated. Given the absence of refined ab initio computed potential energy surfaces and the impracticality of quantum-mechanical calculations for the considered molecular system, theoretical values of these broadening coefficients are estimated by a semi-classical approach with exact trajectories and a model interaction potential including both long-range and short-range (atom-atom) interactions of the active molecule rigorously treated as a symmetric top. It is shown that the short-range forces yield important contributions to the collisional line width for all values of the rotational quantum numbers J and K. Various models are also tested for the isotropic part of the interaction potential which governs the relative translational motion. It is demonstrated that for the very light perturbing molecule H₂ the calculated line widths, practically independent from the rotational quantum number J (for K?≤?J), are particularly sensitive to the position and slope of the repulsive wall. Modifications required in the semi-classical formalism for a correct application of the cumulant expansion are also tested and it is stated that no difference is observed for the CH₃Cl–H₂ system characterised by quite weak interactions.     

Pressure-induced line broadening for the (30012)←(00001) band of CO2 measured with tunable diode laser photoacoustic spectroscopy

Pressure-induced foreign-broadening lineshape parameters of the carbon dioxide rovibrational transitions belonging to the (30012)←(00001) overtone band near the 1.573 μm wavelength region are measured by using a tunable diode laser photoacoustic spectrometer. The spectroscopic analysis has concerned the first 11 lines of the R branch. For these lines, the air- and Ar-broadening coefficients are measured at room temperature (∼298 K). The measured broadening coefficients of all the transitions of ¹²C¹⁶O₂ are compared with those given in the HITRAN04 database and former measurements with a different spectroscopic method. Agreements and discrepancies are underlined and briefly discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficient of carbon dioxide transitions.