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In high orbital angular momentum (ℓ ≥ 3) Rydberg states, the centrifugal barrier hinders the close approach of the Rydberg electron to the ion-core. As a result, these core-nonpenetrating Rydberg states can be well described by a simplified model in which the Rydberg electron is only weakly perturbed by the long-range electric properties (i.e., multipole moments and polarizabilities) of the ion-core. We have used a long-range model to describe the vibrational autoionization dynamics of high-ℓ Rydberg states of nitric oxide (NO). In particular, our model explains the extensive angular momentum exchange between the ion-core and the Rydberg electron that had been previously observed in vibrational autoionization of f (ℓ = 3) Rydberg states. These results shed light on a long-standing mechanistic question around these previous observations and support a direct, vibrational mechanism of autoionization over an indirect, predissociation-mediated mechanism. In addition, our model correctly predicts newly measured total decay rates of g (ℓ = 4) Rydberg states because for ℓ ≥ 4, the non-radiative decay is dominated by autoionization rather than predissociation. We examine the predicted NO+ ion rotational state distributions generated by vibrational autoionization of g states and discuss applications of our model to achieve quantum state selection in the production of molecular ions. [ABSTRACT FROM AUTHOR]

We report calculations of vibrational autoionization rates of CaF Rydberg states, based on the results of a global multi-channel quantum defect theory (MQDT) fit. Our goal is to use intuitive physical models to interpret and extend the results from the MQDT calculations and, in particular, to characterize the physical mechanisms for the interaction between the Rydberg electron and the ion-core. The calculations indicate that, among the six strongly l-mixed core-penetrating (CP) Rydberg series of CaF, the n.36 p ^ Π Rydberg series has the fastest Δ v = 1 vibrational autoionization rate, which is at least four times larger than that for the other CP Rydberg series, in agreement with experimental results. We first demonstrate that the rotational level dependence of the vibrational autoionization rate of the n.36 p ^ Π series is satisfactorily explained by l-uncoupling interactions, which differ for the positive and negative Kronig symmetry levels. Next, we interpret the relative vibrational autoionization rates of all six CP Rydberg series in the context of a valence-precursor (VP) model. The VP model is a consequence of Mulliken's rule, which states that the innermost lobe of the Rydberg wavefunction remains invariant in both the nodal position and shape for members of the same Rydberg series. The electronic properties of the six VP states, which are the terminus states (lowest-n) of each of the six CP Rydberg series, are further characterized in terms of a ligand-field model, providing insight into the intimate relationship between the Rydberg electron density in the ion-core region and the vibrational autoionization rate. [ABSTRACT FROM AUTHOR]

The dependence of multipole moments and polarizabilities on external fields appears in many applications including biomolecular molecular mechanics, optical non-linearity, nanomaterial calculations, and the perturbation of spectroscopic signatures in atomic clocks. Over a wide range of distances, distributed multipole and polarizability potentials can be applied to obtain the variation of atom-centered atoms-in-molecules electric properties like bonding-quenched polarizability. For cylindrically symmetric charge distributions, we examine single-center and atom-centered effective polarization potentials in a non-relativistic approximation for Rydberg states. For ions, the multipole expansion is strongly origin-dependent, but we note that origin-independent invariants can be defined. The several families of invariants correspond to optimized representations differing by origin and number of terms. Among them, a representation at the center of dipole polarizability optimizes the accuracy of the potential with terms through 1/r4. We formulate the single-center expansion in terms of polarization-modified effective multipole moments, defining a form related to the source-multipole expansion of Brink and Satchler. Atom-centered potentials are an origin independent alternative but are limited both by the properties allowed at each center and by the neglected effects like bond polarizability and charge flow. To enable comparisons between single-center effective potentials in Cartesian or spherical form and two-center effective potentials with differing levels of mutual induction between atomic centers, we give analytical expressions for the bond-length and origin-dependence of multipole and polarizability terms projected in the multipole and polarizability expansion of Buckingham. The atom-centered potentials can then be used with experimental data and ab initio calculations to estimate atoms-in-molecules properties. Some results are given for BaF+ and HF showing the utility and limitations of the approach. More detailed results on X ¹∑+ CaF+ are published separately. [ABSTRACT FROM AUTHOR]

Because of their central importance in chemistry and biology, water molecules have been the subject of decades of intense spectroscopic investigations. Rotational spectroscopy of water vapor has yielded detailed information about the structure and dynamics of isolated water molecules, as well as water dimers and clusters. Nonlinear rotational spectroscopy in the terahertz regime has been developed recently to investigate the rotational dynamics of linear and symmetric-top molecules whose rotational energy levels are regularly spaced. However, it has not been applied to water or other lower-symmetry molecules with irregularly spaced levels. We report the use of recently developed two-dimensional (2D) terahertz rotational spectroscopy to observe high-order rotational coherences and correlations between rotational transitions that were previously unobservable. The results include twoquantum (2Q) peaks at frequencies that are shifted slightly from the sums of distinct rotational transitions on two different molecules. These results directly reveal the presence of previously unseen metastable water complexes with lifetimes of 100 ps or longer. Several such peaks observed at distinct 2Q frequencies indicate that the complexes have multiple preferred bimolecular geometries. Our results demonstrate the sensitivity of rotational correlations measured in 2D terahertz spectroscopy to molecular interactions and complexation in the gas phase. [ABSTRACT FROM AUTHOR]

We present an improved quantum defect theory model for the 's,' 'p,' 'd,' and 'f' Rydberg series of CaF. The model, which is the result of an exhaustive fit of high-resolution spectroscopic data, parameterizes the electronic structure of the ten ('s'Σ, 'p'Σ, 'p'Π, 'd'Σ, 'd'Π, 'd'Δ, 'f'Σ, 'f'Π, 'f'Δ, and 'f'[uppercase_phi_synonym]) Rydberg series of CaF in terms of a set of twenty μℓℓ′(Λ) quantum defect matrix elements and their dependence on both internuclear separation and on the binding energy of the outer electron. Over 1000 rovibronic Rydberg levels belonging to 131 observed electronic states of CaF with n* ≥ 5 are included in the fit. The correctness and physical validity of the fit model are assured both by our intuition-guided combinatorial fit strategy and by comparison with R-matrix calculations based on a one-electron effective potential. The power of this quantum defect model lies in its ability to account for the rovibronic energy level structure and nearly all dynamical processes, including structure and dynamics outside of the range of the current observations. Its completeness places CaF at a level of spectroscopic characterization similar to NO and H2. [ABSTRACT FROM AUTHOR]

The Stark effect in molecular Rydberg states is qualitatively different from the Stark effect in atomic Rydberg states because of the anisotropy of the ion core and the existence of rotational and vibrational degrees of freedom. These uniquely molecular features cause the electric-field-induced decoupling of the Rydberg electron from the body frame to proceed in several stages in a molecule. Because the transition dipole moment among the same-n* Rydberg states is much larger than the permanent dipole moment of the ion core, the decoupling of the Rydberg electron from the ion core proceeds gradually. In the first stage, analyzed in detail in this paper, l and N are mixed by the external electric field, while N+ is conserved. In the further stages, as the external electric field increases, N+, n*, and v+ are expected to undergo mixing. We have characterized these stages in n*=13, v+=1 states of CaF. The large permanent dipole moment of CaF+ makes CaF qualitatively different from the other molecules in which the Stark effect in Rydberg states has been described (H2, Na2, Li2, NO, and H3) and makes it an ideal testbed for documenting the competition between the external and CaF+ dipole electric fields. We use the weak-field Stark effect to gain access to the lowest-N rotational levels of f, g, and h states and to assign their actual or nominal N+ quantum number. Lowest-N rotational levels provide information needed to disentangle the short-range and long-range interactions between the Rydberg electron and the ion core. We diagonalize an effective Hamiltonian matrix to determine the l-characters of the 3≤=l≤=5 core-nonpenetrating 2Σ+ states and to characterize their mixing with the core-penetrating states. We conclude that the mixing of the l=4, N-N+=-4(g(-4)) state with... [ABSTRACT FROM AUTHOR]

Observation and analysis of the f(ℓ=3), g(ℓ=4), and h(ℓ=5) Rydberg series of CaF in the range 13≤=n≤=17 is presented. Simultaneous analysis of the f, g, and h Rydberg series of CaF, combined with significant improvements to the long-range model for nonpenetrating Rydberg states, provides a generally applicable scheme for separating the effects of the long-range (electric multipole and polarization) and short-range (core penetration) interactions between the Rydberg electron and ion core in diatomic molecules. Techniques for rigorous assignment of nonpenetrating states, as well as extensions of the long-range model, are discussed. Explicit formulas for the first- and second-order matrix elements of the first four anisotropic electric multipole interactions (electric dipole, quadrupole, octupole, and hexadecapole) are given. The discrepancies between the observed behavior and that predicted by the long-range model, which are particularly significant for the f series, are shown to be due to penetration of the Rydberg electron wavefunction within the ion core. We show that these penetration effects can be understood within the framework of ligand field theory and conclude with a discussion of the relative contributions of the long- and short-range interactions to the quantum defects of the core-penetrating “s,” “p,” and “d” series of CaF. [ABSTRACT FROM AUTHOR]

Results of ab initio R-matrix calculations [S. N. Altunata et al., J. Chem. Phys. 123, 084319 (2005)] indicate the presence of a broad shape resonance in electron-CaF+ scattering for the 2Σ+ electronic symmetry near the ionization threshold. The properties of this shape resonance are analyzed using the adiabatic partial-wave expansion of the scattered electron wave function introduced by Le Dourneuf et al. [J. Phys. B 15, L685 (1982)]. The qualitative aspects of the shape resonance are explained by an adiabatic approximation on the electronic motion. Mulliken’s rule for the structure of the Rydberg state wave functions [R. S. Mulliken, J. Am. Chem. Soc. 86, 3183 (1964)] specifies that, except for an (n*)-3/2 amplitude scale factor, every excited state wave function within one Rydberg series is built on an innermost lobe that remains invariant in shape and nodal position as a function of the excitation energy. Mulliken’s rule implies a weak energy dependence of the quantum defects for an unperturbed molecular Rydberg series, which is given by the Rydberg-Ritz formula. This zero-order picture is violated by a single 2Σ+ CaF Rydberg series at all Rydberg state energies (n*=5→∞, more so with increasing n*) below the ionization threshold, under the broad width of the shape resonance. Such a violation is diagnostic of a global “scarring” of the Rydberg spectrum, which is distinct from the more familiar local level perturbations. [ABSTRACT FROM AUTHOR]

We report a new form of microwave optical double-resonance spectroscopy called millimeter-wave-detected, millimeter-wave optical polarization spectroscopy (mmOPS). In contrast to other forms of polarization spectroscopy, in which the polarization rotation of optical beams is detected, the mmOPS technique is based on the polarization rotation of millimeter waves induced by the anisotropy from optical pumping out of the lower or upper levels of the millimeter wave transition. By monitoring ground-state rotational transitions with the millimeter waves, the mmOPS technique is capable of identifying weak or otherwise difficult-to-observe optical transitions in complex chemical environments, where multiple molecular species or vibrational states can lead to spectral congestion. Once a transition is identified, mmOPS can then be used to record pure rotational transitions in vibrationally and electronically excited states, with the resolution limited only by the radiative decay rate. Here, the sensitivity of this nearly-background-free technique is demonstrated by optically pumping the weak, nominally spin-forbidden CS e 3Σ--X 1Σ+ (2-0) and d 3Δ-X 1Σ+ (6-0) electronic transitions while probing the CS X 1Σ+ (v″=0,J″=2-1) rotational transition with millimeter waves. The J′=2,N′=2←J′=1,N′=1 pure rotational transition of the CS e 3Σ- (v′=2) state is then recorded by optically preparing the J′=1,N′=1 level of the e 3Σ- (v′=2) state via the J′=1,N′=1←J″=1 transition of the e 3Σ--X 1Σ+ (2-0) band. [ABSTRACT FROM AUTHOR]

An ab initio R-matrix method for determining the molecular reaction matrix of scattering theory is introduced. The method makes use of a principal-value Green function to compute the collision channel wave functions for the scattered electron, in combination with the Kohn variational scheme for the evaluation of R-matrix eigenvalues on a spherical boundary surface at short range. This technique permits the size of the bounded volume in the variational calculation to be reduced, making the computations fast and efficient. The reaction matrix is determined in a form that minimizes its energy dependence. Thus the procedure does not require modification or an increase in the computational effort to study the electronic structure and dynamics in Rydberg molecules with extremely polar ion cores. The analysis is specialized to examine the bound-state and free-electron scattering properties of nearly one-electron molecular systems, which are characterized by a Rydberg/scattering electron incident on a closed-shell ion core. However, it is shown that the treatment is compatible with all-electron/ab initio representations of open-shell and nonlinear polyatomic ion cores, emphasizing its generality. The introduced approach is used to calculate the electronic spectrum of the calcium monofluoride molecule, which has the extremely polar (Ca+2F-)+e- closed-shell ion-core configuration. The calculation utilizes an effective single-electron potential determined by M. Arif, C. Jungen, and A. L. Roche [J. Chem. Phys. 106, 4102 (1997)] previously. Close agreement with experimental data is obtained. The results demonstrate the practical utility of this method as a viable alternative to the standard variational approaches. [ABSTRACT FROM AUTHOR]

The ab initio K matrix method described in the preceding paper (Part I) is applied to the Rydberg electronic structure of calcium monofluoride. The spectroscopic quantum defects for the 2Σ+, 2Π, 2Δ, and 2[uppercase_phi_synonym] states of CaF are computed using the effective potential of Arif et al. [M. Arif, Ch. Jungen, and A. L. Roche, J. Chem. Phys. 106, 4102 (1997)]. Satisfactory agreement with the experimental values is obtained. The eigenquantum defects obtained from the reaction matrix for the CaF++e- system are found to be strongly energy dependent. The analysis shows that the main features of the energy-dependent structure in the eigenphases are a consequence of a broad molecular shape resonance. Partial-l (orbital angular momentum) characters of two interacting collision eigenchannels vary rapidly as a function of increasing collision energy. This prominent variation leads to interference structure in the intensities for transitions into the ionization continuum, manifesting nodal points in the total ionization cross section in the continuum above the shape resonance. The usefulness of this structure in the ionization cross section as a direct probe of the l-character of the bound state is discussed. In addition, ab initio results for the photoelectron angular distribution and the anisotropy parameter are presented. These computed results are susceptible to direct experimental verification. [ABSTRACT FROM AUTHOR]

High-resolution (0.013 cm-1) spectra of the second overtone of the OH stretch of trans-nitrous acid were recorded between 10 230 and 10 350 cm-1. The spectra were analyzed to yield a complete set of rotational parameters, including the A, B, and C rotational constants and the 5 quartic distortion constants. Two groups of anharmonic perturbations were observed and analyzed, and for one of these groups, the spectra were fit with a second model to extract an improved set of parameters that took into account these interactions. Much less information could be obtained from our spectra about the second group of perturbations, except that the same dark vibrational state was probably not responsible for both groups of perturbations. The anharmonic coupling matrix element between the 3ν[sub 1] “bright” state and one “dark” vibrational state was found to be 0.0338(31) cm-1, and possible assignments for the “dark” level are discussed. In addition, we report the first measurement of the absolute intensity of the 3ν[sub 1] overtone band, which was found to be 2.1±0.6×10[sup -21] cm[sup 2] molecule[sup -1] cm[sup -1]. Our findings are discussed in the context of the contribution of overtone-mediated processes to OH radical production in the upper atmosphere. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An infrared double-resonance laser spectroscopic technique is used to study state-resolved rotational (R–R, R–T) energy transfer in ammonia (14NH3) (self-collisions and between ammonia and foreign gases). NH3 molecules are prepared in selected rovibrational states of the v2=1 level using coincidences between CO2 -laser lines and ν2 fundamental transitions. Measurements of both the total rate of depopulation by collisions, and the rates of transfer into specific final rovibrational states (v,J,K) have been carried out using time-resolved tunable diode laser absorption spectroscopy. For NH3–NH3 collisions, measurements of total depopulation rates of selected JK states in v2=1 and ground-state recovery rates are found to be three and eight times larger, respectively, than the Lennard-Jones collision rate, in accord with theoretical expectations for polar molecules.A kinetic master-equation analysis of time-resolved level populations yields state-to-state rate constants and propensity rules for NH3–NH3 and NH3–Ar collisions. Individual rotational energy-transfer rates in v2=1 are slower than in the vibrational ground state, but still comparable to the Lennard-Jones collision frequency. Our experiments show that rotational energy transfer in v2=1 is not governed by simple ‘‘dipolelike’’ selection rules. They show fast rotational energy transfer, which can be related to long-range interaction potentials, but at the same time considerable amounts of ΔJ=2 and 3, ΔK=0, and ΔJ=1–4, ΔK=3, transitions, which may be attributed to higher-order terms in the multipole expansion of the intermolecular potential. No pronounced symmetry-state correlation and no preferred pathways were found except the preference for relaxation within a K stack and the expected separate relaxation of different nuclear-spin species, which can be labeled by their K-quantum number. Rates of... [ABSTRACT FROM AUTHOR]

This paper reports analytical approximations to the level-spacing distributions for two types of eigenspectra: a Gaussian orthogonal ensemble (GOE) eigenspectrum, a fraction of whose levels are omitted, and the superposition of a fractional GOE distribution with levels from a random sequence. The combined distribution would be expected when a spectrum with a GOE spacing distribution is observed, but with insufficient dynamic range to observe all the lines, and with the possibility of contamination from other sequences or from noise identified as spectral lines. Berry recently demonstrated that GOE type spacing statistics are expected in the semiclassical limit of a classically chaotic Hamiltonian. Therefore, the present formula may prove useful in testing for quantum signatures of classical chaos in quantum molecular spectra. [ABSTRACT FROM AUTHOR]

Optical transitions to the 2B2 electronic state region of NO2 have been observed in double resonance with three millimeter-wave ground state rotational transitions. The probed ground state transitions were the N=2 (F1), N=4 (F1), and N=10 (F2), K=0→1 Q branch transitions near 250 GHz. The optical range scanned was 16 800 to 16 950 cm-1. The 100,10–101,9 F2 spectrum was combined with previous double resonance results with the ground state 91,9–100,10 F1 transition. This comparison shows 70 out of 160 upper states with J=19/2 to have indefinite or mixed N values. It establishes violations of the ΔN=ΔJ selection rule in this spectral region which contains bands with a wide range of spin-rotation constants. Lack of intensity correlation between the two spectra suggests two classes of upper states are present: a group of strongly N-mixed upper states, and a group essentially unmixed in N. Heller’s F parameter, which measures the fraction of all possible symmetry-restricted basis states contributing to a typical eigenstate, is similar for the double-resonance spectra of the three N values, but is greater for K=1 than for K=0. By finding upper states in common, R lines from N=2 and P lines from N=4 have been identified. [ABSTRACT FROM AUTHOR]

The five and six quanta bands of the N–H overtone bands of NH3, with origins near 15 450 and 18 110 cm-1, respectively, have been rotationally analyzed. Assignments of 318 and 105 lines in the two regions have been made on the basis of microwave-detected microwave-optical double resonance spectra and of photoacoustic absorption spectra. Both regions contain hybrid bands with parallel and perpendicular components which show Coriolis interactions between the optically bright components, and frequent, generally patternless, interactions with background dark vibrational states. These interactions cause almost all lines to be broken into several components. The five quanta region also shows a strong Fermi interaction, suggested due to 4νN–H+3νa2, which causes a negative inversion splitting in the upper states. The relative strengths of the parallel and perpendicular bands are (0.3:0.7) and (0.35:0.65) for the five and six quanta regions, in contrast to lower energies where parallel bands are weak or absent. The band structure can be qualitatively explained on the basis of a local mode description as the A and E states with five and with six quanta of stretch in one of the N–H bonds. Rotational constants of these bands can be well predicted from projections based on the single quanta excitations in contrast to the bands lower in energy. [ABSTRACT FROM AUTHOR]

In a recent paper, Hardwick predicted that the optical spectrum of NO2 should display ‘‘quantum ergodicity’’, meaning that almost all eigenstates allowed by total symmetry should be seen in absorption. We have performed a test of this prediction by using the technique of microwave detected, microwave–optical double resonance. We have determined the spectrum over the range 16 810–17 100 cm-1 for the two ground vibrational states 91,9(F1) and 100,10(F1) of NO2. We observed 324 transitions from the 100,10 state and 364 transitions from the 91,9 state. The number of observed transitions is a factor of 8 greater than that expected if only the allowed rotational transitions to any B2 symmetry vibronic level were observed. The number of observed lines is a factor of 3 less than the number predicted if all selection rules were broken as predicted by Hardwick. Thus we see that Hardwick’s ‘‘ergodicity’’ conjecture is a useful starting point for understanding the spectrum of NO2, but the spectrum is intermediate between the regular and the ergodic limits. [ABSTRACT FROM AUTHOR]

Discusses techniques for pattern recognition and extraction, extended cross correlation (XCC) and extended auto correlation (XAC). Ability to identify and extract multiple patterns from experimental data; Multidimensional forms of the XCC technique; Use of the XCC on large data sets with multiple patterns.

Describes the extended cross correlation (XCC), a pattern recognition technique for large, high quality spectroscopic data sets. Use of spectra for decoding; Motivation for and construction of the XCC; Application of the XCC.

Microwave detected, microwave-optical double resonance was used to record the A state electronic spectrum of NH3, NH2D, and NHD2 with both vibrational and rotational resolution. To investigate ND3 with the same resolution as we had with our hydrogen containing isotopomers, a strip-line cell was constructed allowing the simultaneous passage of radio-frequency and ultraviolet radiation. Rotational constants were obtained as a function of ν2 excitation and an A state equilibrium bond length was estimated at 1.055(8) Å. In addition, the harmonic force field for the à state has been experimentally determined. fhh, fαα-fαα’, and frr were found to be 1.06(4) aJ/Å2, 0.25(2) aJ, and 4.9 aJ/Å2, respectively. This calculated harmonic force field predicts that the asymmetry observed in the NH3 24 band is due to a strong anharmonic interaction with the 43 level and the broad feature observed in the dispersed fluorescence spectrum previously assigned to the 11 band is more likely attributable to the 42 level. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using microwave detected, microwave-optical double resonance, we have measured the homogeneous linewidths of individual rovibrational transitions in the A state of NH3, NH2D, NHD2, and ND3. We have used this excited state spectroscopic data to characterize the height of the dissociation barrier and the mechanisms by which the molecule uses its excess vibrational and rotational energies to help overcome this barrier. To interpret the observed vibronic widths, a one dimensional, local mode potential has been developed along a N–H(D) bond. These calculations suggest the barrier height is roughly 2100 cm-1, approximately 1000 cm-1 below the ab initio prediction. The observed vibronic dependence of levels containing two or more quanta in ν2 is explained by a Fermi resonance between 2ν2 and the N–H(D) stretch. This interaction also explains the observed trends due to isotopic substitution. The rotational enhancement of the predissociation rates in the NH3 21 level is dominated by Coriolis coupling while for the same level in ND3, centrifugal effects dominate. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We propose a stability criterion applicable to eigenstates of approximate Hamiltonians. We define a ‘‘robustness’’ of the physical properties of the underlying system under a variety of internal and external conditions that can be deduced from stability properties of the eigenstates of the approximate Hamiltonian. Stability properties are assigned to an ensemble of eigenstates according to the statistics of its response to an ensemble of random perturbations of given magnitude. The stability criterion is explicitly formulated for the eigenstates of polyatomic molecules exhibiting a normal to local mode transition. As an example, a stability analysis for the water molecule is carried out and experiments in the low density gas phase (rotational energy transfer), high density gas phase (collision-induced spectra), and condensed phase are suggested. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A time-resolved infrared double-resonance technique has been used to measure vibrationally and rotationally inelastic collision rates in ground and vibrational overtone levels of methane. A Raman-shifted Ti:sapphire laser is used to pump J=0 through 7 states in the 2ν3 and ν3+ν4 levels of 12CH4, and a tunable diode laser is used to probe the time-dependent level populations. Vibrational equilibration is observed among the octad, pentad, and dyad levels, with subsequent relaxation to the ground state. State-to-state rotational energy transfer rates are obtained in the ground and ν3+ν4 excited vibrational levels, and compared with theoretical predictions and with pressure-broadening measurements on the corresponding transitions. The probability of molecular reorientation in an inelastic collision is also inferred from the polarization dependence of the relaxation times. Parity-conserving and vibrational angular momentum propensity rules are inferred for the lower rotational levels of methane. © 1994 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We argue that the physical significance of the normal to local mode transition in triatomic molecules AB2 lies in an enhanced susceptibility of eigenstates to symmetry breaking perturbations. States of local character have higher susceptibilities than states of normal character. The quantum mechanical condition for the normal to local mode transition is formulated. The issue of stability is addressed from a classical, semiclassical, and quantum mechanical point of view. The question of instability of the unperturbed quantum system is decided individually for each eigenstate. The relevance for experiments is outlined. [ABSTRACT FROM AUTHOR]

Acetylcarnitine has been identified as one of several urinary biomarkers indicative of radiation exposure in adult rhesus macaque monkeys (non-human primates, NHPs). Previous work has demonstrated an up-regulated dose-response profile in a balanced male/female NHP cohort. As a contribution toward the development of metabolomics-based radiation biodosimetry in human populations and other applications of acetylcarnitine screening, we have developed a quantitative, high-throughput method for the analysis of acetylcarnitine. We employed the Sciex SelexIon DMS-MS/MS QTRAP 5500 platform coupled to flow injection analysis (FIA), thereby allowing for fast analysis times of less than 0.5 minutes per injection with no chromatographic separation. Ethyl acetate is used as a DMS modifier to reduce matrix chemical background. We have measured NHP urinary acetylcarnitine from the male cohorts that were exposed to the following radiation levels: control, 2, 4, 6, 7, and 10 Gy. Biological variability, along with calibration accuracy of the FIA-DMS-MS/MS method, indicates LOQ of 20 µM, with observed biological levels on the order of 600 µM and control levels near 10 µM. There is an apparent onset of intensified response in the transition from 6 to 10 Gy. The results demonstrate that FIA-DMS-MS/MS is a rapid, quantitative technique that can be utilized for the analysis of urinary biomarker levels for radiation biodosimetry. [ABSTRACT FROM AUTHOR]

The coherence relaxation rate (T2) of the J=0 –1 transition of 15N2O has been examined using microwave transient techniques. The transient decays were analyzed by a model which considers the absorber speed dependence of the collisional relaxation process [S. L. Coy, J. Chem. Phys. 73, 5531 (1980)]. The decays were also analyzed by the standard speed independent model. In the speed dependent analysis, a linear absorber speed dependence of the form k(v)=k0+k1(v-v), where v is the Boltzmann average speed, was assumed. Values of k0=0.0300(1) μs-1 mTorr-1 and k1v=0.0099(4) μs-1 mTorr-1 were determined. In the speed independent analysis a relaxation rate, k=0.029 22(6) μs-1 mTorr-1, was found. This corresponds to a pressure broadening parameter 1/2πT2 of 4.65(1) MHz/Torr. A zero pressure transition frequency and pressure dependent frequency shift parameter were also determined. They are 24 274.7865(1) MHz and +30(4) kHz/Torr, respectively. The experimental uncertainties reported above are two standard errors from linear least squares fits of k, k0, k1v, and transition frequency, vs sample pressure. The most significant systematic error is a 1% uncertainty in the pressure calibration which contributes an additional 1% error to the slopes determined from the linear least squares fits. [ABSTRACT FROM AUTHOR]

RATIONALE There is continued interest in exploring new analytical technologies for the detection and quantitation of DNA adducts, biomarkers which provide direct evidence of exposure and genetic damage in cells. With the goal of reducing clean-up steps and improving sample throughput, a Differential Mobility Spectrometry/Mass Spectrometry (DMS/MS) platform has been introduced for adduct analysis. METHODS A DMS/MS platform has been utilized for the analysis of dG-ABP, the deoxyguanosine adduct of the bladder carcinogen 4-aminobiphenyl (4-ABP). After optimization of the DMS parameters, each sample was analyzed in just 30 s following a simple protein precipitation step of the digested DNA. RESULTS A detection limit of one modification in 10^6 nucleosides has been achieved using only 2 µg of DNA. A brief comparison (quantitative and qualitative) with liquid chromatography/mass spectrometry is also presented highlighting the advantages of using the DMS/MS method as a high-throughput platform. CONCLUSIONS The data presented demonstrate the successful application of a DMS/MS/MS platform for the rapid quantitation of DNA adducts using, as a model analyte, the deoxyguanosine adduct of the bladder carcinogen 4-aminobiphenyl. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Forensic drug laboratories are inundated with cases requiring time-consuming GC- or LC-based chromatographic separations of submitted samples. High-throughput analytical methods would be of great practical utility within forensic drug analysis. Recently developed ion-mobility-based separation methods combined with mass spectrometry can often be used without chromatography, suppress chemical interferents of similar mass, and operate in seconds. We have evaluated differential mobility spectrometry-mass spectrometry (DMS-MS) for performance on adulterated cocaine mixtures. The DMS interface is only a few centimeters in length, operates in seconds, and can be adapted to any MS system using atmospheric pressure ionization. Drug cutting agents, typical targets such as cocaine, and drug metabolites are rapidly separated by the DMS ion prefilter. Tests demonstrated characterization of complex mixtures, such as isolation of levamisole, an adulterant with alarming side effects, from a 13-component mixture. DMS-MS holds great potential for the analysis of drug samples submitted for forensic analysis. [ABSTRACT FROM AUTHOR]

Purpose: Radiation exposure triggers a complex network of molecular and cellular responses that impacts metabolic processes and alters the levels of metabolites. Such metabolites have potential as biomarkers for radiation dosimetry. This review provides an overview of radiation signalling and metabolism, of metabolomic approaches used in the discovery phase, and of instrumentation with the potential to assess radiation injury in the field. Approach: Recent developments in fast, high-resolution chromatography and mass spectrometry and new data analysis methods allow the quantitative assessment of thousands of metabolites based on biofluids obtained non-invasively. This complex analysis leads to the discovery-phase identification of groups of metabolites useful for screening and biodosimetry by targeted quantitative measurement. Instrumentation for target analysis can be simpler than that used for discovery, so we examine current technologies based on ion mobility. Conclusions: Recent published results and ongoing studies examine the complex changes in the levels of many metabolites caused by radiation exposure, and identify groups of small-molecule biomarkers for radiation biodosimetry. Based on results showing separation orthogonal to mass, chemical noise suppression, and high sensitivity, differential mobility mass spectrometry (DMS-MS) ion mobility spectrometry appears highly promising for the development of deployable instrumentation. [ABSTRACT FROM AUTHOR]

Devices based on differential mobility spectrometry (DMS) are used in a number of ways, including applications as ion prefilters for API-MS systems, as detectors or selectors in hybrid instruments (GC-DMS, DMS-IMS), and in standalone systems for chemical detection and identification. DMS ion separation is based on the relative difference between high field and low field ion mobility known as the alpha dependence, and requires the application of an intense asymmetric electric field known as the DMS separation field, typically in the megahertz frequency range. DMS performance depends on the waveform and on the magnitude of this separation field. In this paper, we analyze the relationship between separation waveform and DMS resolution and consider feasible separation field generators. We examine ideal and practical DMS separation field waveforms and discuss separation field generator circuit types and their implementations. To facilitate optimization of the generator designs, we present a set of relations that connect ion alpha dependence to DMS separation fields. Using these relationships we evaluate the DMS separation power of common generator types as a function of their waveform parameters. Optimal waveforms for the major types of DMS separation generators are determined for ions with various alpha dependences. These calculations are validated by comparison with experimental data. [ABSTRACT FROM AUTHOR]

The interaction between electronic and rotational motions in the Rydberg states of calcium monofluoride is investigated using multichannel quantum defect theory (MQDT). By examining the partial-ℓ and N+ composition of the molecular wavefunctions of successive members of each of the Rydberg series, we show that the nature of the interaction between the motion of the Rydberg electron and the rotational motion of the ion core undergoes complex and non-monotonic changes with increasing principal quantum number n* and total angular momentum N. Resonances between the Kepler motion of the Rydberg electron and the rotational motion of the ion core (the 'stroboscopic effect') are observed when the Kepler period is an integer multiple of the rotational period. These resonances result in strong mixing of both the electron orbital angular momentum ℓ and the ion core rotational angular momentum N+. At n* or N values between these resonances, the angular momenta of the electron and ion core subsystems are more nearly conserved. We also find evidence for a second type of resonance, which takes place between the precessional motion of the Rydberg electron and the rotation of the core. The qualitative features of these various dynamical regimes can be explained in terms of the classical frequencies of motion of the electron and ion and the nature of the electrostatic interactions between them. The results presented here provide general insights into the interaction between electronic and rotational motions in both polar and non-polar diatomic molecules. [ABSTRACT FROM AUTHOR]

We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of Rydberg-Rydberg transitions is that they have enormous electric dipole transition moments (∼5 kiloDebye at n* ∼ 40, where n* is the effective principal quantum number), so they interact strongly with the mm-wave radiation. After polarization by a mm-wave pulse in the 70-84 GHz frequency region, the excited transitions re-radiate free induction decay (FID) at their resonant frequencies, and the FID is heterodyne-detected by the CPmmW spectrometer. Data collection and averaging are performed in the time domain. The spectral resolution is ∼100 kHz. Because of the large transition dipole moments, the available mm-wave power is sufficient to polarize the entire bandwidth of the spectrometer (12 GHz) in each pulse, and high-resolution survey spectra may be collected. Both absorptive and emissive transitions are observed, and they are distinguished by the phase of their FID relative to that of the excitation pulse. With the combination of the large transition dipole moments and direct monitoring of transitions, we observe dynamics, such as transient nutations from the interference of the excitation pulse with the polarization that it induces in the sample. Since the waveform produced by the mm-wave source may be precisely controlled, we can populate states with high angular momentum by a sequence of pulses while recording the results of these manipulations in the time domain. We also probe the superradiant decay of the Rydberg sample using photon echoes. The application of the CPmmW technique to transitions between Rydberg states of molecules is discussed. [ABSTRACT FROM AUTHOR]

A correction to the article "A quantum defect model for the s, p, d, and f Rydberg series of CaF" which was published in the 2011 issue is presented.

Presents a correction to the article 'Rotational Structure of Ammonia N-H Stretch Overtones: Five and Six Quanta Bands,' by Stephen L. Coy and Kevin K. Lehmann, which appeared in the 1986 issue of the 'Journal of Chemical Physics.'