Raúl Z. Martínez

Linewidths of C2H2 perturbed by H2: experiments and calculations from an ab initio potential

In this work we present a theoretical and experimental study of the acetylene-hydrogen system. A potential surface considering rigid monomers has been obtained by ab initio quantum chemistry methods. This 4-dimensional potential is further employed to compute, using the close-coupling approach and the coupled-states approximation, pressure broadening coefficients of C2H2 isotropic Raman Q lines over a temperature range of 77 to 2000 K. Experimental data for the acetylene nu2 Raman lines broadened by molecular hydrogen are obtained using stimulated Raman spectroscopy. The comparison of theoretical values with experimental data at 143 K is promising. Approximations to increase the computational efficiency are proposed.

Raman and infrared linewidths of CO in Ar

We present measurements of Raman linewidths in the fundamental Q branch of CO for mixtures with Ar at temperatures of 77, 195, and 300 K, recorded using an inverse Raman spectrometer. Starting from a recent ab initio potential energy surface, theoretical values of Ar broadening coefficients for CO infrared and Raman lines (isotropic and anisotropic components) at temperatures in the range 77 to 1100 K are calculated via quantum-mechanical methods. The relative merits of the close coupling theoretical results over the coupled states results are underlined. Finally, a comparison of the calculated pressure broadening coefficients is made with the present experimental data as well as with recently available infrared data. There is general agreement between the calculated and measured values of the broadenings for all the temperatures probed. We conclude that the temperature dependence of the infrared and Raman broadening coefficients have been correctly determined theoretically and may be used to test a commo...

High resolution Raman spectroscopy from vibrationally excited states populated by a stimulated Raman process: 2ν1−ν1 of CH412

A new pump and probe technique for investigating vibrationally excited states via high resolution Raman spectroscopy is proposed. In a first step, a vibrational state, typically not accessible by a dipole moment transition from the ground state (IR forbidden, Raman allowed transition), is populated in a doubly pulsed stimulated Raman process. This state is long lived as the radiative decay to the ground state is highly inefficient. After a delay of several nanoseconds, the high resolution spectrum corresponding to a transition from this excited level is recorded. The second process follows the quasi-cw stimulated Raman spectroscopy scheme reported previously. Experimental aspects are discussed and the spectrum of 2ν1−ν1 of 12CH4 is presented as an illustration of the technique. The analysis of this spectrum has been done in two ways: first, by fitting simultaneously the ν1 and 2ν1 bands using an isolated band model; second, using a model based on the tetradecad-pentad system. The standard deviations of bo...

High resolution Raman spectroscopy from vibrationally excited states populated by a stimulated Raman process. Transitions from v2=1 in 12C2H2 and 13C2H2

The Raman spectra of the Q branches of the ν1+ν2−ν2 band of 12C2H2 and of the ν1+ν2−ν2 and 2ν2+2ν5−ν2 bands of 13C2H2 were recorded at high resolution in the gaseous phase. To obtain the spectra a two-step pump/probe technique was used. In the first step, molecules were pumped from the ground to the v2=1 excited state by means of a double pulsed stimulated Raman process. Then, spectra corresponding to the transitions from this state to higher ones are recorded by means of a high resolution quasicontinuous stimulated Raman process. The analysis of the experimental data, taking into account the fourth-order anharmonic interaction coupling the excited states for the 13C isotopomer, provided unperturbed values for the rotational and distortion constants of the excited states and for the band origins. Accurate values for the x120 anharmonicity constant have been calculated directly from the energies of the v1=v2=1 states for the first time.

High resolution infrared and Raman spectroscopy of ν 2 and associated combination and hot bands of 13C12CD2

Infrared and Raman spectra of dideuterated acetylene containing one 13C atom, 13C12CD2, have been recorded and analysed to obtain detailed information on the fundamental ν 2 band and associated combination and hot bands. Infrared spectra were recorded at 4 × 10−3 cm−1 resolution in the region 1150−2900 cm−1, which contains combination and hot bands from the ground and the bending v 4 = 1 and v 5 = 1 states. The Q-branches of the ν 2 fundamental and associated hot bands (ν 2 + ν 4 − ν 4, ν 2 + ν 5 − ν 5, ν 2 + 2ν 4 − 2ν 4, ν 2 + 2ν 5 − 2ν 5 and ν 2 + ν 4 + ν 5 − (ν 4 + ν 5)) were recorded using inverse Raman spectroscopy, with an instrumental resolution of about 3 × 10−3 cm−1. In addition, the observation of the 2ν 2 − ν 2 Raman band was carried out populating the v 2 = 1 state by stimulated Raman pumping. In total, 11 Raman and 9 infrared bands were analysed, involving all the l-vibrational components of the excited stretching−bending manifolds up to v t  = v 4 + v 5 = 2. A simultaneous analysis of all infrared and Raman assigned transitions has been performed on the basis of a theoretical model which takes into account the rotation and vibration l-type resonances within each vibrational manifold and the Darling−Dennison anharmonic resonance between the ν 2 + 2ν 4 and ν 2 + 2ν 5 states. The parameters obtained reproduce the assigned transition wavenumbers with a standard deviation of the same order of magnitude as the experimental uncertainty.

Close coupling calculations for rotational relaxation of CO in argon: Accuracy of energy corrected sudden scaling procedures and comparison with experimental data

Fully quantal scattering calculations are carried out for CO in argon using both the close coupling (CC) and coupled states (CS) methods. CC and CS cross sections σ(j→j′) generally agree to within 15% or less with the exception of those corresponding to low Δj=|j′−j| values at low j where differences may reach 50%. The discrepancy arises mostly from efficient collisions with large orbital angular momentum, where the rotation of the quantization axis can no longer be neglected. Then, the CC calculations were used to test a scaling procedure based on the energy corrected sudden (ECS) approximation: given a set of basic cross-section σ(j→0), is it possible to predict the entire σo(j→j′) relaxation matrix? The ECS procedure yields reasonable agreement, on average, at the 13% level. However it fails at reproducing the Δj=1 cross sections in cases where the concept of a mean adiabaticity factor losses its physical meaning since the duration of the efficient collisions varies too much with the orbital angular mo...

The v2, v3 and 2v10 Raman bands of ethylene (12C2H4)

Abstract The Raman spectrum of 12C2H4 has been recorded in the 1343–1347cm−1, 1617–1626cm−1 and 1651–1664cm−1 regions using an inverse Raman technique with an instrumental resolution of about 3×10−3cm−1. The Q branches of V3 (CH2 bending, Ag) at 1343.31 cm−1, V2 (CC stretching, A g ) at 1626.17 cm−1 and 2v10 (overtone of CH bending in plane, A g ) at 1664.16 cm−1, were observed and analysed. The recorded bands are of type A, and the selection rules for the transitions are ΔJ=0, ΔK a =0 and ΔK C =0 since only Q branches are strong enough to be observed. The v 2 and 2v10 bands are perturbed owing to a Fermi interaction between the V 2 =1 and v10=2 states, the latter being in turn perturbed by the v 7 =v 10=1 state, at about 1780 cm−1, through a z(a)-type Coriolis interaction. The V3 band has been analysed taking into account the y(c)-type Coriolis interaction between the v3=1 and V 6 =1 levels. Although the v6 fundamental and v 7 +v 10 combination bands have not been detected, their origins and rotational c...Doubly stochastic, magic square, and alternating sign matrices are matrices of order n over the set of real positive numbers , the set of nonnegative numbers , and the set of integers {−1,0,1}, respectively, having fixed row and columns sums of 1, an arbitrary positive integer N, and 1. Each can be expressed as a sum over permutation matrices of order n with coefficients that belong to , to the positive integers , and to , respectively. Mathematically, these objects are basic in combinatorics; physically, they arise in several contexts that are briefly reviewed. Little has been developed on their expansions in terms of permutation matrices, and little is known about counting formulas for them, except for alternating sign matrices where a closed formula for arbitrary n was recently obtained through the work of Zeilberger. Expansions of these matrices in terms of permutation matrices can be used to investigate and develop their properties. Such an expansion is called a representation of the magic square. Representations are, however, not unique, and the problem arises of enumerating the number of distinct representations of one and the same magic square. The present investigation addresses this problem in the context of primitive magic squares, which are defined as the class of magic squares of order n having a unique representation in which each permutation matrix occurs exactly once in the expansion, and such that this uniqueness is destroyed by the addition of another permutation matrix not already in the representation, a property called completeness. The set of primitive magic squares has a rich structure that is invariant under the action of a group G that is isomorphic to the dihedral group. The group G is definitive in unveiling the general structure of primitive magic squares by providing a complete labelling scheme that utilizes the (n − 4)-fold direct product group of G and a binary tree that specifies a path that shows how the elements in the direct product group are to be selected. Based on this structure, a recurrence relation is derived that generates all inequivalent primitive magic squares. The recurrence relation itself shows a hidden structure of more basic magic squares, called universal kernels, that underlie the structural form of all primitive magic squares. The recurrence relation for primitive magic squares is thus shifted to a recurrence relation for the universal kernels that is simpler in form, which is also derived. These recurrence relations produce one and the same primitive magic square in multiple ways, and the sorting out of the distinct magic squares thus generated remains a problem that is not yet solved.

Communication: Observation of homonuclear propensity in collisional relaxation of the 13C12CD2 (v2 = 1) isotopologue of acetylene by stimulated Raman spectroscopy

We report the first experimental observation of homonuclear propensity in collisional relaxation of a polyatomic molecule. A pump-probe stimulated Raman setup is used to pump population to a single rotational level of the v(2) = 1 vibrationally excited state in (13)C(12)CD(2) and then monitor the redistribution of the rotational population that has taken place after a fixed delay. The Q-branch of the 2ν(2)-ν(2) band shows a pattern of intensity alternation between the even and the odd rotational components, with the greater intensities always corresponding to the rotational levels with the same parity as the one where all the population was initially deposited. The effect can be explained by the existence of a propensity rule that favors collisional relaxation between rovibrational levels of the same parity.

Direct determination of state-to-state rotational energy transfer rate constants via a Raman-Raman double resonance technique: ortho-acetylene in v2=1 at 155 K

A new technique for the direct determination of state-to-state rotational energy transfer rate constants in the gas phase is presented. It is based on two sequential stimulated Raman processes: the first one prepares the sample in a single rotational state of an excited vibrational level, and the second one, using the high resolution quasi-continuous stimulated Raman-loss technique, monitors the transfer of population to other rotational states of the same vibrational level as a function of the delay between the pump and the probe stages. The technique is applied to the odd-J rotational states of v(2)=1 acetylene at 155 K. The experimental layout, data acquisition, retrieval procedures, and numerical treatment are described. The quantity and quality of the data are high enough to allow a direct determination of the state-to-state rate constant matrix from a fit of the experimental data, with the only conditions of detailed balance and of a closed number of states. The matrix obtained from this direct fit is also compared with those obtained using some common fitting and scaling laws.

Bacteremia caused by nonhemolytic group B streptococci

Case Report A 75-yr-old woman with a history of type 2 noninsulin-dependent diabetes and hepatic cirrhosis with previous acute episodes of encephalopathy was admitted to the hospital because of abdominal swelling, tenderness of several day’s duration, and nausea On physical examination, the patient was afebrile and had tender hepatomegaly, ascites, and jaundice with normal central nervous system findings. The white blood cell count was 8,100/mm3 (85% neutrophils, 12% lymphocytes, and 3% monocytes). Prythrocyte sedimentation rate was 102 mm at the first hour. Other hematologic studies, metabolic profile, and liver function tests showed increased serum amylase (2,832 U/L), hyperglycemia, and hyperbilirubinemia An ultrasonogmphic study was done and a clinical diagnosis of acute pancreatitis was confiied. Medical therapy was begun, and the disease was self-limited within 3 d after treatment was instituted On the fifth day after admission, the patient underwent gynecological exploration because of vaginal discomfort, and a sample of the purulent vaginal discharge was sent to microbiology laboratory for culture. On the sixth day, she suddenly developed fever (39”C), and three sets of blood cultures were obtained. Empiric treatment with cefotaxime (2 g tid i.v.) was begun, yet the patient remained febrile. The vaginal sample grew a pure culture of a gram-positive, nonhemolytic coccus subsequently identified as Sneptoc0ccus agalactiue (3). The same microorganism also grew in all three blood culture sets after overnight incubation (BacTAlert system, Organon Teknika). A Gram stain of the blood culture showed gram-positive cocci resembling streptococci. The organism grew on sheep blood agar at 37°C with 5% COZ as small, white, slightly convex, nonhemolytic colonies, and hemolysis was not detectable on lifting a colony from the agar. The isolate was catalase-negative, PYRand bile esculin-negative, bacitracin-resistant, and did not grow in the presence of 6.5% sodium chloride. In addition, positive reactions for voges-Proskauer and hippurate hydrolysis tests were obtained. Group B streptococcal antigen was demonstrated with the PhadeBact test system (Karo Bio Diagnostics, Sweden), and a biochemical profile consistent with group B streptococci was obtained with the API 20 Strep test (bioM&ieux, France). Serotyping of the isolate by agglutination with antisera to GBS serotypes I through V (Dako A/S, Denmark) produced agglutination with the type II antisera. Repeated subcultures of the isolate onto blood agar under aerobic and anaerobic conditions failed to produce beta hemolysis. No pigment production was seen when the isolate was cultured in Granada medium, a selective and differential pigmentenhancing culture medium (4).