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15 Feb 1988

Volume 88, Issue 4, pp. 2099-2863

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Rotationally resolved double resonance spectra of NO Rydberg states near the first ionization limit

D. Therese Biernacki, Steven D. Colson, and E. E. Eyler

J. Chem. Phys. 88, 2099 (1988); http://dx.doi.org/10.1063/1.454091 (9 pages) | Cited 36 times

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Optical–optical double resonance multiphoton ionization spectroscopy is used to study several Rydberg states of nitric oxide with the A(3sσ) 2Σ+, v=1 state as an intermediate level. These v=1 Rydberg states include the 8s, 9s, 7f, 8f, and 8p, but no d states are observed. The states are rotationally resolved due to the capability of optical–optical double resonance experiments to select particular rotational levels of the intermediate state. A rotationally analysis of the data for the 8s and 9s states yields values for the rotational constant, the centrifugal distortion constant, and the term energy of the lowest rotational level for each state. Analysis of the data for the 7f and 8f states yields values for the ion core quadrupole moment, polarizability and rotational constant, and a correction for core penetration. These constants are obtained by a generalized least‐squares fit to a long‐range interaction model for electrostatic forces between the ion core and the Rydberg electron. The 8p, v=1 state is perturbed, probably by an interaction with the 5f, v=2 state. One example of quantum interference between the 5f level with v=2, N=4, and L=−3, and the 8p 2Σ+, v=1, N=4 level has been analyzed.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)
33.20.Sn Rotational analysis
31.50.Df Potential energy surfaces for excited electronic states

Millimeter and submillimeter wave spectroscopy of protonated and deuterated nitrous oxide

Marcel Bogey, Claire Demuynck, and Jean‐Luc Destombes

J. Chem. Phys. 88, 2108 (1988); http://dx.doi.org/10.1063/1.454092 (4 pages) | Cited 2 times

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The a‐ and b‐type rotational spectra of the protonated and deuterated nitrous oxide have been investigated in the millimeter and submillimeter frequency range. The molecular ions were produced in a magnetically confined glow discharge. The comparison between the accurate molecular constants deduced from the analysis of the spectra and different sets deduced from ab initio calculations gives structural information on the observed species: the experimental spectra belong to the O‐protonated and ‐deuterated nitrous oxide.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Laser spectroscopy of calcium and strontium monoazide free radicals

C. R. Brazier and P. F. Bernath

J. Chem. Phys. 88, 2112 (1988); http://dx.doi.org/10.1063/1.454093 (5 pages) | Cited 7 times

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We have synthesized the gas‐phase metal azides CaN3 and SrN3. These ionic metal monoazides were found to have linear geometries. The positions of the math2Π–math 2Σ+ and math 2Σ+–math 2Σ+ electronic transitions were determined as well as several vibrational frequencies. The 0–0 band of the math 2Π–math 2Σ+ system of SrN3 has been rotationally analyzed by laser excitation spectroscopy yielding a Sr–N bond length of 2.26 Å.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Sn Rotational analysis
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants

High‐resolution laser spectroscopy of strontium isocyanate, SrNCO

L. C. O’Brien and P. F. Bernath

J. Chem. Phys. 88, 2117 (1988); http://dx.doi.org/10.1063/1.454094 (4 pages) | Cited 6 times

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The 0–0 band of the math 2Π–math 2Σ+ transition of the linear free radical strontium monoisocyanate, SrNCO, was recorded at high resolution. By comparing the molecular constants of SrNCO with related molecules, the NCO− ligand was found to be nitrogen bonding to the strontium atom. The spectrum is extremely dense because of the small rotational constant, B″=0.0426 cm−1, and overlapping sequence structure. The Sr–N bond length was estimated to be 2.26 Å in the ground math 2Σ+ state.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Sn Rotational analysis
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants

Infrared flash kinetic spectroscopy of HCO

C. Brent Dane, D. R. Lander, R. F. Curl, F. K. Tittel, Yili Guo, Martin I. F. Ochsner, and C. Bradley Moore

J. Chem. Phys. 88, 2121 (1988); http://dx.doi.org/10.1063/1.454095 (8 pages) | Cited 22 times

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The high resolution infrared spectrum of the CH stretching fundamental of the formyl radical (HCO) has been observed by means of infrared kinetic spectroscopy using 308 nm (XeCl) excimer laser flash photolysis of formaldehyde or acetaldehyde followed by diode or difference frequency laser probing of the transient absorption. The high resolution spectra obtained were assigned and fitted with rotational, spin–rotational, and centrifugal distortion constants. The ν1 band origin is 2434.48 cm−1. New ground‐state constants are reported from a least‐squares fit combining this ν1 data with previous microwave and FIR LMR measurements.
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33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis

ESR spectrum of I17O2: Asymmetric hyperfine tensor of 17O

J. R. Byberg

J. Chem. Phys. 88, 2129 (1988); http://dx.doi.org/10.1063/1.454045 (6 pages) | Cited 3 times

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ESR spectra of I 17O2 embedded in solid KC104 exhibit a complicated 17O hyperfine structure, which allows an accurate determination of the hyperfine and quadrupole tensors A(17O) and Q(17O). A(17O) is strongly anisotropic in the molecular plane and contains an asymmetric component. These unexpected features are accounted for in terms of second‐order contributions to A(17O) arising from cross terms of the spin–orbit coupling and the orbital and spin dipole hyperfine interaction. The second‐order terms also contribute substantially to the hyperfine tensor of the iodine nucleus.
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33.35.+r Electron resonance and relaxation
32.10.Fn Fine and hyperfine structure

A relaxation time study of SF5 reorientation in solid tetrakis (pentafluorosulfanyl) hydrazine, (SF5)2NN(SF5)2

M. R. Choudhury, J. W. Harrell, J. B. Nielsen, and J. S. Thrasher

J. Chem. Phys. 88, 2135 (1988); http://dx.doi.org/10.1063/1.454046 (4 pages) | Cited 1 time

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An experimental and theoretical study of the 19F relaxation in solid tetrakis (pentafluorosulfanyl) hydrazine due to the reorientation of the SF5 groups has been undertaken. T1 and T1ρ have been measured from 138 to 292 K. T1 is very long, reaching a maximum of 1140 s at the lowest temperature for one sample, and is determined primarily by paramagnetic impurities. T1ρ appears to be influenced by paramagnetic impurities below 227 K and determined by the reorientation of the SF5 groups above 227 K. Expressions for T1 and T1ρ have been derived for two different reorientational models. In the first model the SF5 group is assumed to undergo 90° jumps about the C4 axis; whereas, in the second model the SF5 group is assumed to undergo rotational diffusion about the C4 axis. The T1ρ measurements above 227 K have been fit to the derived expressions to obtain the correlation time for the reorientation.
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76.60.Es Relaxation effects
61.50.-f Structure of bulk crystals

2H‐NMR study of the glass transition in supercooled ortho‐terphenyl

Th. Dries, F. Fujara, M. Kiebel, E. Rössler, and H. Sillescu

J. Chem. Phys. 88, 2139 (1988); http://dx.doi.org/10.1063/1.454047 (9 pages) | Cited 64 times

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The glass forming molecular liquid ortho‐terphenyl has been investigated by 2H‐NMR techniques providing spin‐relaxation times (T1, T2), and spin‐alignment data which yield information on the time scale and geometry of ultra‐slow molecular reorientation. The main results are as follows: The primary glass transition (α process) is characterized by rotational molecular jumps with a jump size distribution weighted in favor of large jump angles, and by a distribution of correlation times. In addition intramolecular flip–flop jumps of the lateral phenyl rings are found which do not take part in the α process. Apart from this (secondary) intramolecular dynamics no residual small angle reorientation persists below Tg on the time scale (10−4 to 102 s) of the spin‐alignment experiment.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
76.60.Es Relaxation effects

Half‐collision studies of the Hg–NH3 excimer

M. C. Duval, Benoit Soep, Roger D. van Zee, Wayne B. Bosma, and Timothy S. Zwier

J. Chem. Phys. 88, 2148 (1988); http://dx.doi.org/10.1063/1.454734 (11 pages) | Cited 24 times

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The Hg–NH3 complex has been studied by forming the complex in a supersonic jet and probing the bound‐to‐bound transitions to the two excited electronic states correlated to Hg(6 3P1)+NH3. Laser‐induced fluorescence and action spectroscopy have been combined with isotopic studies to map out the characteristics of these states. Both excited states are found to be bound by more than 5000 cm−1, over 20 times greater than the ground state binding energy. Extensive vibrational structure is found and interpreted in terms of a stretching progression of the Hg–NH3 bond and bending of the NH3 moiety with respect to the mercury atom. The two states show striking differences in their behavior with respect to predissociation to Hg(6 3P0). The math state is not observed in fluorescence, but predissociates efficiently to Hg(3P0)+NH3, while the math state shows predominant fluorescence with only a minor amount of Hg(6 3P0) formation. Rotational band contour analysis has been used to assign the math state as the 3E and the math state as the 3A1 state. Both states are characterized by a shortening in the Hg–N bond distance from 3.35 Å in the ground state to about 2.2 Å in either excited state. The rotational contour assignments show that the electronic angular momentum of the excited mercury atom is preserved in the complex despite the complex’s polyatomic nature. This allows an interpretation of the electronic relaxation in a quasidiatomic fashion. All our results are consistent with a C3v geometry for the Hg–NH3 complex in both the ground and excited states. The characteristics of the math and math states and their couplings to the math state correlated to 3P0 enable a comparison with the full‐collision studies and has led us to postulate the math and math states as the source of the luminescence observed in those studies.
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33.50.Dq Fluorescence and phosphorescence spectra
33.20.Tp Vibrational analysis

Dependence of the N2 vibrational potential on density

Ray Engelke

J. Chem. Phys. 88, 2159 (1988); http://dx.doi.org/10.1063/1.454048 (3 pages)

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Recently, part of the vibrational spectrum of the ground electronic (X 1∑+g) state of condensed phase N2, shocked to high density, has been measured by Schmidt, Moore, and Shaw. Densities (ρ) of nearly three times the ambient liquid value were obtained in the shock wave experiments. Due to the high temperatures achieved behind the shock waves, up to six vibrational levels of N2 were observed. These vibrational spectra show clear frequency shifts from their ambient condition values. Here, these experimental spectra are used to infer changes in the vibrational potential of N2 due to the high density environment. The vibrational portion of the Rydberg–Klein–Rees (RKR) method is used to do this. We find that, in the range of densities studied, the energies [E(n;ρ)] of the first five vibrational transitions of N2 can be accurately represented by E(n;ρ)=ωe(ρ)(n+ 1/2 )−ωexe(n+ 1/2 )2, where ωe(ρ)=ω0e+A[1−(ρ0/ρ)1/3] and ωexe is a constant which is independent of the thermodynamic state of the environment; here, ω0e and A are fitting constants and ρ0 and ρ are the ambient (liquid) and shocked densities of N2. Given E(n;ρ), one can obtain the classical turning point difference, r12, of the N2 potential as a function of n and ρ by using the RKR procedure. It is found that at the highest shock density observed (2.13 g/cm3), the relative change in r12 from the ambient condition values is about −1% for the first six vibrational levels.
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78.30.C- Liquids
33.20.Tp Vibrational analysis

Orientation‐selective 14N electron spin echo envelope modulation (ESEEM): The determination of 14N quadrupole coupling tensor principal axis orientations in orientationally disordered solids

Heather L. Flanagan, Gary J. Gerfen, Albert Lai, and David J. Singel

J. Chem. Phys. 88, 2162 (1988); http://dx.doi.org/10.1063/1.454049 (7 pages) | Cited 11 times

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We present an orientation‐selective ESEEM (electron spin echo envelope modulation) technique. From a measurement of the variation of the amplitudes of modulation components at 14N pure quadrupole frequencies as a function of irradiation position within an EPR (electron paramagnetic resonance) powder pattern, we determine the orientation of the principal axes of the quadrupole coupling tensor relative to the principal axes of the tensor which governs the dispersion of the EPR spectrum in an orientationally disordered sample. The pure quadrupole frequencies appear when the EPR frequency is selected such that the nuclear Zeeman and the hyperfine interaction are approximately equal in magnitude. We have applied the method to a mercaptoethanol complex of myoglobin in which the pure quadrupole frequencies originate from 14N in the proximal imidazole ring. Our results enable us to validate the assignment of the quadrupole modulations to the metal‐coordinated nitrogen of the imidazole ring, to correlate the principal axes with the principal values of the quadrupole coupling tensor, and to determine the orientation of the imidazole ring relative to the principal axes of the (low‐spin) Fe(III) g matrix. These findings are discussed and compared with results of previous studies.
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76.70.Dx Electron-nuclear double resonance (ENDOR), electron double resonance (ELDOR)
76.30.-v Electron paramagnetic resonance and relaxation

Ring torsional dynamics and spectroscopy of benzophenone: A new twist

John H. Frederick, Eric J. Heller, Judy L. Ozment, and David W. Pratt

J. Chem. Phys. 88, 2169 (1988); http://dx.doi.org/10.1063/1.454050 (16 pages) | Cited 39 times

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The low energy portion of the high resolution S1←S0 fluorescence excitation spectrum of benzophenone recently reported by Holtzclaw and Pratt [J. Chem. Phys. 84, 4713 (1986)] is modeled here using a simple two‐degree‐of‐freedom vibrational Hamiltonian. The Hamiltonian features a 1:1 nonlinear resonance between the two low frequency ring torsional modes of the molecule in its S1 state. Line positions and intensities of the two major spectral progressions are well reproduced using parameters similar to those derived from earlier matrix diagonalizations. The comparison of the theory and experiment results in a determination of the displacement of the S1 surface relative to the ground electronic state along the symmetric torsional coordinate and permits a calculation of the excitation spectra of various isotopically substituted molecules not yet measured in the laboratory. A clear picture of the relationship between the dynamics on the S1 surface and the spectroscopy of benzophenone is revealed by comparing a time domain analysis of the experimental data with wave packet dynamics on the model S1 surface. This comparison provides new insight into energy flow in the isolated molecule and permits a qualitative simulation of the effects of collisional quenching on the fluorescence spectrum. We also discuss, using a classical trajectory analysis, the resonance dynamics of the torsional modes and note the existence of heretofore undetected local modes in the high resolution spectrum.
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33.20.Lg Ultraviolet spectra
33.50.Dq Fluorescence and phosphorescence spectra
33.20.Tp Vibrational analysis
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Structure and vibrational dynamics of the CO2 dimer from the sub‐Doppler infrared spectrum of the 2.7 μm Fermi diad

K. W. Jucks, Z. S. Huang, R. E. Miller, G. T. Fraser, A. S. Pine, and W. J. Lafferty

J. Chem. Phys. 88, 2185 (1988); http://dx.doi.org/10.1063/1.454051 (11 pages) | Cited 90 times

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Sub‐Doppler infrared spectra of two Fermi resonance coupled bands of carbon dioxide dimer have been obtained at 3611.5 and 3713.9 cm−1 using an optothermal molecular beam color‐center laser spectrometer. The band origins for the complexes are red shifted by approximately 1 cm−1 from the corresponding ν1+ν3/2ν02+ν3 CO2 bands. The higher frequency band is perturbed while the lower frequency band appears free of extraneous perturbations as determined from a precision fit to a Watson asymmetric rotor Hamiltonian. This fit and the observed nuclear spin statistical weights reveal that the complex is planar with C2h symmetry. The C‐‐C separation and C‐‐C–O angle are determined to be 3.599(7) Å and 58.2(8)°, respectively. The nearest neighbor O‐‐C distance is 3.14 Å which is the same as that found in the crystal. From the centrifugal distortion analysis the weak bond stretching and symmetric bending frequencies are estimated to be 32(2) and 90(1) cm−1. No interconversion tunneling is observed.
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36.40.-c Atomic and molecular clusters
33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis

Near infrared spectroscopic observation of the linear and cyclic isomers of the hydrogen cyanide trimer

K. W. Jucks and R. E. Miller

J. Chem. Phys. 88, 2196 (1988); http://dx.doi.org/10.1063/1.454052 (9 pages) | Cited 60 times

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Sub‐Doppler resolution infrared spectra have been obtained for both the linear and cyclic conformers of the hydrogen cyanide trimer. In the case of the linear trimer, all three vibrational bands correlating with the C–H stretching fundamental of the hydrogen cyanide monomer (ν1) have been observed. The vibrational predissociation lifetime of the complex is found to be strongly mode specific. For the cyclic trimer, which has only one (doubly degenerate) infrared allowed band associated with the C–H stretch, the rotational structure is characteristic of an oblate planar symmetric top. Molecular constants are reported for both conformers. In addition, several other bands are observed in the spectrum which, although not rotationally resolved, are tentatively assigned to the tetramer.
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36.40.-c Atomic and molecular clusters
33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Semiclassical phase space evolution of Fermi resonance spectra

Michael E. Kellman and Eric D. Lynch

J. Chem. Phys. 88, 2205 (1988); http://dx.doi.org/10.1063/1.454053 (11 pages) | Cited 25 times

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The evolution of the semiclassical phase space of a Fermi resonance spectrum is investigated as the strength of the resonance coupling is varied between zero and the strong coupling limit. The phase space evolution gives information beyond that contained in the phase space profile of the experimental spectrum alone. The zero‐order phase space is found to be different in important respects from that of the pendulum model of a nonlinear resonance. In the weak coupling regime, the phase space evolution is essentially like that of a dynamical barrier picture. In the strong coupling regime of ‘‘intrinsic resonance,’’ the phase space structure is much different. Topology change appears to take place in a more discontinuous manner than in the weak coupling regime. The phase space evolution shows that some levels are problematic for an adiabatic switching treatment. The origin of some anomalous levels seen both in phase space profiles of experimental spectra and in semiclassical quantization studies is clarified.
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33.20.Tp Vibrational analysis
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Coupling interaction between the sulfate ion ν2 modes and the lithium modes in LiKSO4

Seung‐Bin Kim and Roger Frech

J. Chem. Phys. 88, 2216 (1988); http://dx.doi.org/10.1063/1.454054 (10 pages) | Cited 2 times

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Resonant couplings between the sulfate ion ν2 mode and the lithium ion translatory mode in E2 and E1 symmetries have been studied in single crystal 7 LiKSO4 and 6 LiKSO4 from polarized Raman spectra between 298 and 519 K and from infrared reflectivity spectra at room temperature. Coupling effects are negligible in 7 LiKSO4 whereas in 6 LiKSO4 the lithium isotope effect shifts the lithium translatory mode into resonant coupling with the sulfate ion ν2 mode. The resonant coupling mechanism between the two fundamental E2 modes is elucidated by a comparative analysis of the temperature dependence of the frequency shifts and the relative intensities. The coupling interaction in E1 symmetry can be only qualitatively described due to poor resolution of the Raman bands. It is possible to distinguish anharmonic processes which couple two modes from anharmonic processes which perturb each state individually. It was found that coupling anharmonicity decreased while perturbative anharmonicity increased with increasing temperature. Detailed consideration of various intensity ratios in E2 symmetry allows the separation of the isotope effect from the coupling contribution to the polarizability derivative tensor. In E1 symmetry TO–TO and LO–LO coupling interactions between the ν2 mode of the sulfate ion and the lithium translatory mode were deduced from the frequency and intensity data.
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78.30.Hv Other nonmetallic inorganics

ESR investigation of the cation radicals 14N2 13CO+, 15N2 12CO+, and 15N2 13CO+: The trapping of ion–neutral reaction products in neon matrices at 4 K

Lon B. Knight, J. Steadman, P. K. Miller, and J. A. Cleveland

J. Chem. Phys. 88, 2226 (1988); http://dx.doi.org/10.1063/1.454055 (9 pages) | Cited 9 times

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ESR results are reported for the cation radicals 15 N212 CO+ , 15 N213 CO+ and 14 N213 CO+ trapped as isolated ions in neon matrices at 4 K. The N2CO+ radical was generated by codepositing N2 and CO into a neon matrix under ionizing conditions (both photoionization at 16.8 eV, and 50 eV electron bombardment). A complete resolution of the 14 N, 15 N, and 13 C A tensors reveal that the radical is planar and nonlinear (NNC O). Electronic structure changes that occur as N+2 and CO (or CO+ with N2) combine to form N2CO+ are analyzed by comparing the nuclear hfs of the diatomic reactants with that of the product radical. The 13C hfs is extremely large with Ax =1376(1); Ay =1407(1), and Az =1403(1) MHz. The A tensor for the inner 14 N atom is: Ax,y =200.2(6) and Az =226.6(3) MHz. The outer 14 N has ‖Ax,y‖ =4(1) and Az =9.4(2) MHz. The nuclear g tensor appears axially symmetric with gx,y=2.0007(3) and gz =2.0002(3). SCF calculations also show N2 CO+ to be nonlinear and yield A values in reasonably good agreement with experiment. These ESR results for N2CO+ are compared with similar measurements for the isoelectronic ions C2O+2, N+4, and C2N−2.
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76.30.Rn Free radicals
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
33.35.+r Electron resonance and relaxation
33.15.Pw Fine and hyperfine structure

Direct excitation studies of the diffuse bands of alkali metal dimers

Wei‐Tzou Luh, John T. Bahns, A. Marjatta Lyyra, Kenneth M. Sando, Paul D. Kleiber, and William C. Stwalley

J. Chem. Phys. 88, 2235 (1988); http://dx.doi.org/10.1063/1.454056 (7 pages) | Cited 21 times

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Direct dye laser excitations of the K2 yellow, Rb2 orange, and Cs2 near‐infrared diffuse bands have been investigated. Experimental results are shown to be consistent with the assumed bound–free 2 3Πg–1 3∑+u excitations. It is found that for Rb2 and Cs2, spin–orbit interactions become so significant that the 2 3Πg state is strongly split into three quite independent component states.
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36.40.-c Atomic and molecular clusters
33.20.Kf Visible spectra

Optical spectra and energy level analysis of Dy3+:LaCl3

R. S. Rana, J. Shertzer, F. W. Kaseta, R. Garvey, D. Rana, and S. Y. Feng

J. Chem. Phys. 88, 2242 (1988); http://dx.doi.org/10.1063/1.454057 (7 pages) | Cited 6 times

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The absorption spectrum of Dy3+:LaCl3 at 4 K has been photographed and measured from 20 000 to 38 000 cm−1. Based on this and previous data, an empirical energy level scheme consisting of 151 observed crystal levels from 0 to 34 130 cm−1 has been determined for the 4f9 ground configuration of trivalent dysprosium in LaCl3 crystals. An extended Hamiltonian with 20 adjustable parameters is used to fit by least squares the observed levels with a mean error of 6.9 cm−1.
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78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
71.55.Eq III-V semiconductors

High‐resolution photoionization spectrum of water molecules in a supersonic beam

Ralph H. Page, Robert J. Larkin, Y. R. Shen, and Y. T. Lee

J. Chem. Phys. 88, 2249 (1988); http://dx.doi.org/10.1063/1.454058 (15 pages) | Cited 38 times

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We have obtained high‐resolution (∼1.5 cm−1) photoionization spectra of supersonically cooled (Trot∼50 K) H2O and D2O in the 1000–900 Å range. The light source, which used the technique of frequency tripling in a pulsed free jet of gas, is described briefly. Spectra are rotationally resolved. Vibrationally excited autoionizing Rydberg series converging to the ground electronic [math; (1b1)−1] state of the molecular ion are detected. This may well be the first example of a highly resolved Rydberg spectrum of a stable polyatomic molecule. From the convergence limit, the ionization potential H2O is determined to be 101 777±7 cm−1. Intensities of the Rydberg state autoionization signals are smaller than predicted with known Franck–Condon factors, indicating that predissociation is a competitive decay channel. Rydberg state lifetimes are ∼1 ps, deduced from homogeneous linewidths. Autoionizing features from Rydberg states associated with the ion’s quasilinear math (3a1)−1 state are observed with linewidths above 10 cm−1, indicating that their lifetimes are less than ∼0.5 ps. Rotational assignments of some of the bands in this linear←bent transition show that the Rydberg and ionic state geometries are nearly identical. A consistent assignment of the controversial bending (v2) quantum number and Rydberg series quantum defect δ=−0.037 have been provided.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.70.Fd Absolute and relative line and band intensities

First moments of the liquid phase far‐infrared absorption cross section and the R(ω) representation of depolarized Rayleigh scattering

R. Rodriguez and J. L. McHale

J. Chem. Phys. 88, 2264 (1988); http://dx.doi.org/10.1063/1.454059 (9 pages) | Cited 11 times

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A calculation of the first moment or average frequency ω of the liquid phase far‐infrared absorption cross section is presented. The theory also applies to the calculation of the average frequency of the R(ω) representation of depolarized Rayleigh scattering data, where R(ω)=ω[1−exp(−ℏω/kT)]I(ω). The average frequency is shown to depend on the integral of the imaginary part of the angular derivative correlation function divided by time. A semiclassical relationship between the real and imaginary parts of the correlation function is derived and shown to lead to a series representation of ω in terms of fourth and higher moments of the intensity spectrum. It is demonstrated that the theory reproduces the exact semiclassical result for ω of both the far‐IR absorption spectrum and the R(ω) representation of the depolarized Rayleigh wing of linear free rotors. The implications of our theory concerning the comparison of peak frequencies in the far‐IR absorption spectrum and the R(ω) representation of the depolarized Rayleigh scattering spectrum are discussed. The theory is able to qualitatively explain the experimentally observed dependence of peak frequency on temperature, concentration, and isotopic substitution. The ratio of the average frequencies of the absorption cross section and the R(ω) representation is shown to depend on the size of the mean square torque compared to (kT)2.
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78.30.C- Liquids
33.20.Ea Infrared spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Fd Absolute and relative line and band intensities

Concentration dependent depolarized Rayleigh scattering of dimethylformamide‐h7 and ‐d7 in CCl4 solution

R. Rodriguez and J. L. McHale

J. Chem. Phys. 88, 2273 (1988); http://dx.doi.org/10.1063/1.454060 (8 pages) | Cited 4 times

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The formulas derived in our previous paper on the first moments of far‐infrared and depolarized Rayleigh spectra are applied to the study of dimethylformamide (DMF) and its deuterated derivative in carbon tetrachloride solution. Changes in the peak and average frequencies of the R(ω) representation of the depolarized Rayleigh wing data are measured as a function of concentration and compared to limited far‐infrared absorbance spectra of the more dilute solutions. The measured average frequencies of the DRS data agree well with those calculated from the area under the imaginary correlation function divided by time, and with the values calculated from the first term in the series expression for ω in terms of fourth and higher even moments. Collisional contributions to the spectral moments complicate the determination of mean square torques and orientational correlations from the DRS spectra. The first and second moments were found to be larger than the theoretical values for purely reorientational scattering and were fairly independent of concentration. The data suggest that the additional scattering is due to a dipole–induced dipole contribution to the polarizability αi⋅Ti j⋅αj.
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78.30.C- Liquids
78.35.+c Brillouin and Rayleigh scattering; other light scattering

The microwave spectrum of the H2Cl+ ion

Shuji Saito, Satoshi Yamamoto, and Kentarou Kawaguchi

J. Chem. Phys. 88, 2281 (1988); http://dx.doi.org/10.1063/1.454061 (3 pages) | Cited 6 times

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Four rotational transitions of the H2Cl+ ion were observed in the frequency region of 270 to 500 GHz by using a source‐modulated microwave spectrometer combined with a hollow cathode free space cell. The H2Cl+ ion was generated by a dc discharge in a mixture of HCl, H2, and He. The ion was identified on the basis of the hyperfine structure of the chlorine nucleus. This was further confirmed by the observation of the line intensity decrease with external magnetic field, which is a characteristic of ions in a hollow cathode discharge. The rotational constants A, B, and C, and the centrifugal distortion constant ΔJK were determined. The nuclear quadrupole coupling constants of the chlorine nucleus were obtained for the first time: χaa =−53.44(47) MHz, χbb =−15.71(50) MHz, and χcc =69.15(70) MHz with three standard errors in parentheses. The character of the H–Cl bond orbital is estimated from the observed nuclear quadrupole coupling constants and the molecular structure.
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33.20.Bx Radio-frequency and microwave spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

1H shielding anisotropy in Mg(OH)2: The isolated OH− group

R. E. J. Sears, R. Kaliaperumal, and S. Manogaran

J. Chem. Phys. 88, 2284 (1988); http://dx.doi.org/10.1063/1.454062 (5 pages) | Cited 3 times

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The proton NMR shielding tensor was measured at room temperature in the hexagonal layered compound magnesium hydroxide. The isotropic shielding is 29.9±2 and the anisotropy is 12.7±2 ppm, on the 1H absolute scale. From a Gierke and Flygare (GF) analysis of the data the OH− spin–rotation constant was found to be 51±14 kHz. The GF contributions from the neighbors of a given OH− group were subtracted from the experimental shielding and corrections were made for the effects of vibrational motion to give an isotropic shielding of 29.9±2, with an anisotropy of 13.7±2 ppm, for an isolated OH−. The OH− shielding anisotropy is in good agreement with the ab initio calculations of Ratcliffe et al., but the isotropic shielding is not. Proton spin–lattice relaxation measurements at 300 and 77 K gave evidence of proton conductivity in Mg(OH)2.
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76.60.Es Relaxation effects

Comparison of experiment and theory for the resonance Raman spectrum of I2 in solution. IV. Band shapes and hot bands

Roseanne J. Sension and Herbert L. Strauss

J. Chem. Phys. 88, 2289 (1988); http://dx.doi.org/10.1063/1.454063 (7 pages) | Cited 17 times

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Each observed Raman transition of I2 in solution is made up of an overlapping series consisting of the fundamental, or an overtone, and its associated hot bands. As the excitation frequency is changed, these various components change their relative intensities, making it appear that the Raman transition changes frequency. The Raman excitation profiles of the separate transitions have been measured and the results compared to calculations. The results suggest the presence of heretofore uncharacterized I2 states—perhaps charge transfer states—that contribute to the Raman intensity. However, we cannot suggest a specific state that would be consistent with all the experimental results presented in this series of papers.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Jg Line and band widths, shapes, and shifts
33.70.Fd Absolute and relative line and band intensities
78.30.C- Liquids
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