Biomedical subjects

RW Field

Publications and source records attributed to RW Field.

18 recordsLinked to original sources

PubMed2001

The Predissociation of the 1(3)Sigma(-)(g) State of (7)Li(2).

The predissociation of the 1(3)Sigma(-)(g) v >/= 10 levels of (7)Li(2) has been observed by pulsed and continuous-wave perturbation-facilitated optical-optical double-resonance spectroscopy (PFOODR). Our ab initio calculation shows that the inner wall of the 1(3)Sigma(-)(g) potential intersects the 1(3)Pi(g) repulsive potential at internuclear distance R = 2.00 Å. The predissociation is due to a DeltaS = 0, DeltaLambda = +/-1 rotational-electronic interaction with the repulsive 1(3)Pi(g) state. Copyright 2001 Academic Press.

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PubMed2000

Observation of Coriolis Coupling between nu(2) + 4nu(4) and 7nu(4) in Acetylene &Xtilde;(1)Sigma(+)(g) by Stimulated Emission Pumping Spectroscopy.

Stimulated emission pumping (SEP) spectroscopy has been used to examine a low energy region (E(vib) approximately 4400 cm(-1)) of &Xtilde;(1)Sigma(+)(g) acetylene at higher resolution than was possible in previous dispersed fluorescence studies. The expected bright state, nu(2) + 4nu(4), is observed to be coupled to the nearly degenerate 7nu(4) state by a Coriolis mechanism. A least-squares analysis yields values for zero-order vibrational energies, rotational constants, and a Coriolis-coupling coefficient that are all consistent with expectations. Calculated relative intensities of SEP transitions, accounting for interference due to axis-switching effects, are also consistent with observations. Implications of the observed Coriolis resonance with regard to global acetylene vibrational dynamics are also discussed. Copyright 2000 Academic Press.

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PubMed2000

The 2(3)Delta(g) State of (7)Li(2).

Using pulsed perturbation-facilitated optical-optical double resonance (PFOODR) spectroscopy, the 2(3)Delta(g) state of (7)Li(2) (electronic configuration (varsigma(g)2s) (4ddelta(g)), effective principal quantum number n* = 4.101) has been observed and assigned. Molecular constants and a RKR potential energy curve were obtained. The major molecular constants are Copyright 2000 Academic Press.

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PubMed2000

Intensity Measurements and Collision-Broadening Coefficients for the Oxygen A Band Measured by Intracavity Laser Absorption Spectroscopy.

High-sensitivity, high-resolution intracavity laser absorption spectroscopy (ICLAS) has been used to measure line intensities, nitrogen-broadening coefficients, and self-broadening coefficients in the A band (b(1)Sigma(+)(g) <-- X(3)Sigma(-)(g)) of oxygen. Both linear cavity and ring cavity ICLAS configurations were used for these measurements, and the results were intercompared. The results were compared to values measured using long-path multiple-reflection cells by K. D. Ritter and T. D. Wilkinson [J. Mol. Spectrosc. 121, 1-19 (1987)] and L. Brown and C. Plymate, [J. Mol. Spectrosc. 199, 166-179 (2000)]. New results are included for weakly absorbing transitions, not observed in the earlier measurements, such as high rotational states (up to J = 39), hot-band transitions (v' = 1 <-- v" = 1), and isotopically substituted species ((18)O(2) and (16)O(18)O). Isotopic variants ((16)O(2), (18)O(2), and (16)O(18)O) have similar broadening coefficients for corresponding rotational levels, but the self-broadening coefficients are larger in the hot band (v' = v" = 1) as compared with v' = v" = 0 transitions. An ECS-EP scaling analysis of the v' = v" = 0 self-broadening data accurately represents the available data, with the exception of the N = 0 and N = 1 levels. Copyright 2000 Academic Press.

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PubMed1999

Double-Resonance Spectroscopic Studies of Core-Penetrating Rydberg States of CaCl.

Six core-penetrating Rydberg series have been assigned in the CaCl molecule by a combination of double-resonance spectroscopic techniques. Two 2Sigma+ series, with approximate quantum defects (delta) of 0.51 and 0.25, have been observed with effective principal quantum numbers (n*) in the range of 5-8 using the D2Sigma+ state as the resonant intermediate state for REMPI and/or ion-dip detection. A third 2Sigma+ series with delta approximately 0.84 and a 2Delta series with delta approximately 0.95 have been observed with n* = 16-18 using the A2Pi3/2 state as the resonant intermediate state for preparation of v+ = 1 vibrationally autoionizing states. Two additional series in the same region with delta approximately 0.90 and 0.07 are tentatively identified as the expected core-penetrating 2Pi series. Vibrational assignments have been confirmed in many cases on the basis of isotope shifts between the 35Cl and 37Cl isotopomers. The ion-dip and REMPI spectra display linewidths systematically broadened by predissociation. In addition to the assigned core-penetrating series, both the REMPI and the ion-dip spectra display some sharper features that have not yet been assigned. These sharper features most likely arise from perturbations of optically "bright" core-penetrating states by nominally "dark" higher-l core-nonpenetrating states. Copyright 1999 Academic Press.

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PubMed1999

Thermochemical Properties (D degrees0 and IP) of the Lanthanide Monohalides.

Thermochemical data for the lanthanide monohalides have been combined with recent ligand field theory calculations (A. L. Kaledin, M. C. Heaven, R. W. Field, and L. A. Kaledin (1996). J. Mol. Spectrosc. 179, 310) to estimate the dissociation energies and ionization potentials for all LnX (where Ln in Ba through Lu, and X in F, Cl, Br, or I) molecules and the dissociation energies for the LnX+ ions. Owing to the negligible involvement of the core-like 4f electrons in bonding, the dissociation energies and ionization potentials of all LnX molecules, where Ln in Ba through Lu, and X in O, S, F, Cl, Br, or I, should vary with Ln atom in a simple linear manner, provided that corrections are made for differences in f-orbital occupancy between the LnX molecule and the free Ln atom or between the LnX molecule and the LnX+ molecular ion. We provide such a model here and, in so doing, correct several inconsistencies in the thermochemical data. Based on thermochemical data (A. A. Kitaev, I. S. Gotkis, P. G. Val'kov, and K. C. Krasnov (1996). Russ. Chem. Phys. 7, 1685) and recent spectroscopic observations (M. C. McCarthy, J. C. Bloch, R. W. Field, and L. A. Kaledin (1996) J. Mol. Spectrosc. 179, 251), a revised value for the ionization potential of DyF, IP(DyF) = 5.85 +/- 0.06 eV, is proposed. Copyright 1999 Academic Press.

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PubMed1999

The Predissociation Mechanism for 2Sigma+ Rydberg States of CaCl.

This work summarizes experimental results from recent ion-dip spectroscopy studies of CaCl and from previously unpublished optical-optical double-resonance work with specific regard to predissociation processes of 2Sigma+ Rydberg states in the low n* (n* = 7, IP - En* = 2240 cm-1) region. A single repulsive state (assigned as 2Sigma+) was found to be responsible for all observed predissociations of 2Sigma+ Rydberg states. The n*-dependent internuclear distances of the intersections between Rydberg states and the repulsive 2Sigma+ state were determined through the use of trial-and-error Franck-Condon calculations. Values of energy-descaled electronic matrix elements governing the Rydberg left and right arrow repulsive state interaction were obtained from the measured linewidths (0.6 < Gamma < 1.2 cm-1) and computed Franck-Condon densities. Copyright 1999 Academic Press.

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PubMed1999

Rotational Pattern Difference in Resolved Fluorescence Spectra with Different Detection Schemes.

The relative intensities of rotational lines in resolved fluorescence spectra are dependent on the detection direction and the choice of the detection scheme when a grating monochromator is used. These differences arise from the spatially anisotropic distribution of the fluorescence, the rotational branch dependence of the fluorescence polarization, and the polarization dependence of the monochromator grating efficiency. Both the anisotropy of the emission and the rotational branch dependence of the fluorescence polarization are enhanced in double-resonance excitation schemes. In the present work, we analyze the relative intensities in the (7)Li(2) 1(3)Sigma(-)(g) --> 1(b)(3)Pi(u) and 1(3)Delta(g) --> 1(b)(3)Pi(u) resolved fluorescence spectra, observed following double-resonance excitation, for three different detection schemes. Copyright 1999 Academic Press.

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PubMed1999

Analysis and Deperturbation of the A(2)Pi and B(2)Sigma(+) States of CaF.

A laser excitation spectrum of the (0, 0) and (1, 1) bands of the CaF A(2)Pi-X(2)Sigma(+) system was recorded. The present set of molecular constants for both A(2)Pi and B(2)Sigma(&plus:) states represents a vast improvement in precision over previously reported values because of the larger number of line position measurements and the use of a more reasonable effective Hamiltonian model which accounts explicitly for the A approximately B interaction via off-diagonal matrix elements. The principal constants (in cm(-1)) are where uncertainties of 1varsigma are given in parentheses. Copyright 1999 Academic Press.

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PubMed1998

Laser Transient Absorption Spectroscopy of Bromomethylene

We report the observation and assignment of new high-resolution spectra of the A1A" <-- X1A' transition of bromomethylene, HCBr, obtained by transient laser absorption spectroscopy at near-infrared wavelengths. The 2(1)0 band of HCBr (nu0 = 11 957 cm-1) and the 2(2)0 band of DCBr (nu0 = 12 349 cm-1) have been observed for both naturally occurring isotopes of bromine. The c-type rotational branches of the Ka = 0 <-- 1 subbands have been assigned in detail. Other subbands have been partially assigned, but their detailed rotational quantum number analysis has not yet proved possible. Their presence does, however, indicate that the molecule exhibits nonlinear rotational structure in these vibrational levels, in contrast to what was found for the A1A" (0, 2, 0) level of HCBr (nu0 = 12 786 cm-1) [B. C. Chang and T. J. Sears, J. Chem. Phys. 105, 2135-2140 (1996)]. Analysis of the rotational structure in the spectra reported here has required a reassessment of certain rotational assignments of that previous work. We now find that the lower singlet state is isolated; there is no evidence of triplet state perturbations. Rotational constants derived for the ground state of all the naturally occurring isotopomers were used to estimate structural parameters. A barrier to linearity for the A1A" state, 13 590 cm-1 above the zero point level of the ground X1A' state, is estimated. Copyright 1998 Academic Press.

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PubMed1998

The 4(3)Pig and 6(3)Pig States of Na2: Observation and Assignment.

Two 3Pig states of Na2 have been observed in the 35 000-38 000 cm-1 energy region by pulsed perturbation facilitated optical-optical double resonance (PFOODR) fluorescence excitation spectroscopy and assigned to the 5dpi and 6dpi (the fourth and sixth according to the energy rank at Re) 3Pig Rydberg states, respectively. Molecular constants and RKR potential curves are reported. Copyright 1998 Academic Press.

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PubMed1997

The Fluorescence Excitation Spectrum of HCO &Btilde;2A'-&Xtilde;2A', 000 Band

The rotationally resolved laser-induced fluorescence spectrum of the HCO &Btilde;2A'-&Xtilde;2A' transition in the 000 band is observed under thermalized conditions. The formyl radical is produced from acetaldehyde photolyzed at wavelengths 310 or 308 nm. Some spin-splittings of the spectra are resolved. About 988 transitions to Ka' </= 3 and N' </= 24, approximately 94% of the observed lines, are assigned in this work including weak DeltaKa = ±2 transitions that become allowed because of the effects of axis-switching. Copyright 1997Academic Press

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PubMed1997

Laser Frequency-Modulated Spectroscopy of a Laser-Guided Plasma in Sodium Vapor: Line Positions for NaH (A1Sigma+-X1Sigma+), Na (9-13d and 11-14s), and Ar (5p-4s)

Laser frequency-modulated (FM) spectroscopy has been used as an axial probe of a laser-guided electric discharge in sodium-argon vapor contained in an optically accessible metal heat pipe oven. Absorption measurements in the region 23 106-23 881 cm-1 provided accurate line positions (±<0.006 cm-1) for 141 transitions in the v' = 3-8 <-- v" = 0 and v' = 5-9 <-- v" = 1 bands of NaH (A1Sigma+-X1Sigma+). In addition, 18 transitions of Na (3p to 9-13d and 11-14s) and 10 of argon (5p-4s) were measured. Analysis of the spectrum indicates that perhaps all absorption signals are due to neutrals NaH, Na, and Ar and are observed via "population" modulation. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1994