Eizi Hirota

Microwave Spectra, Hyperfine Structure, and Electric Dipole Moments for Conformers I and II of Glycine

A number of low-J rotational transitions have been measured for two conformations of the simplest amino acid, glycine, providing precise hyperfine transition frequencies and electric dipole moments for radioastronomy searches for glycine in interstellar clouds. Measurements were made between 12 and 25 GHz with a pulsed-nozzle, Fabry-Perot-cavity, Fourier transform microwave spectrometer equipped with either a heated nozzle or laser ablation-nozzle for vaporization of solid phase glycine. Nuclear quadrupole coupling constants were determined for both conformers from measurements of the hyperfine-split rotational transitions. The quadrupole coupling constants for conformer I are eQqaa = -1.208(9) MHz and eQqbb = -0.343(8) MHz and for conformer II are eQqaa = 1.773(2) MHz and eQqbb = -3.194(4) MHz. The dipole moment components of both conformers were determined to higher precision. We obtain μa = 3.039(10) × 10-30 C m [0.911(3)D] and μb = 2.025(17) × 10-30 C m [0.607(5) D] for conformer I, and μa = 17.92(11) × 10-30 C m [5.372(34)D] and μb = 3.10(3) × 10-30 C m [0.93(1)D] for conformer II, where the uncertainties shown are 1 standard deviation.

Third-order anharmonic potential constants and equilibrium structures of the formyl and hydroperoxyl radicals

Abstract Observed vibration—rotation constants for HCO/DCO and HO 2 /DO 2 are combined with vibrational frequencies and ground-state rotational constants in order to derive harmonic as well as third-order anharmonic potential constants, and also equilibrium structure parameters for the formyl and hydroperoxyl radicals. The “diagonal” terms of the third-order anharmonic constants thus obtained for the stretching modes are discussed in terms of the diatomic-molecule model.

Vibronic interactions in the NO3 radical

The 1492 cm−1 band of NO3 previously reported [J. Chem. Phys. 82, 2196 (1985); 93, 951 (1990)] exhibits some features in the upper state which are difficult to understand if the band is purely vibrational, i.e., the degenerate N–O stretching band in the ground electronic state. The two most conspicuous anomalies are a finite spin‐orbit coupling term which must be included in the Hamiltonian and a derived first‐order Coriolis coupling constant which is smaller than the calculated value. These anomalous features are explained by the vibronic interaction with excited 2E’ electronic states.

The spectroscopic characterization of the methoxy radical. II. Rotationally resolved A (2)A(1)-X (2)E electronic and X (2)E microwave spectra of the perdeuteromethoxy radical CD(3)O.

Rotationally resolved laser-induced fluorescence (LIF) and stimulated emission pumping (SEP) A (2)A(1)-X (2)E spectra of the perdeuteromethoxy radical (CD(3)O) have been observed. These data directly connect the two spin-orbit components (E(1/2) and E(3/2)) of the ground electronic state with high precision. Molecular constants for both electronic states are determined in a global fitting that involves LIF, SEP, and pure rotational spectra in the microwave region. For the microwave transitions, the resolved hyperfine structure is analyzed providing molecular parameters characterizing it and hyperfine-free transitions for the global fitting. A complete experimental geometry for the methoxy radical at the C(3v) conical intersection is determined from the rotational constants of its isotopologs. The experimental isotopic dependence of other parameters in the effective Hamiltonians is compared to the theoretically expected variation. These comparisons allow considerable insight into the physical significance of a number of parameters in the effective Hamiltonian. In particular, experimental evidence is found for a previously predicted vibrational correction to the A rotational constant of a Jahn-Teller active molecule.

NEAR-INFRARED BAND OF THE NITRATE RADICAL NO3 OBSERVED BY DIODE LASER SPECTROSCOPY

We have analyzed the near-infrared band of NO3 observed at 7602u2009cm−1 by using diode laser spectroscopy. Most of the spectral lines were recorded using source-frequency modulation. Zeeman modulation was found useful in selectively detecting some Q branch lines, which provided us with a clue to the assignment of the observed spectra. The band satisfied selection rules for a parallel band and was thus ascribed to a 2A1″–2A2′ vibronic component associated with the 2E′′–Xu20092A2′ electronic transition, namely, to a transition from the ground vibronic state to the A1″ vibronic state resulting from excitation of the degenerate in-plane bending mode in the 2E′′ electronically excited state manifold. The band was almost free of perturbations, except for some K=6 lines. The least-squares analysis of 581 assigned lines led to molecular parameters of the upper state, where ground-state parameters were fixed to those obtained from the infrared study previously reported [K. Kawaguchi, E. Hirota, T. Ishiwata, and I. Tanak...

High-resolution infrared spectroscopy of NO3 in the 2500-cm−1 region

Abstract The infrared spectroscopic measurement of the NO3 radical has been extended to the 2500-cm−1 region, and two new bands of E-A type were observed around 2518 and 2585 cm−1. The rotational analyses clearly indicated that these bands had the lowest state in common, which coincided with the ground state. The 2518-cm−1 band is very similar to the 1492-cm−1 band reported previously, and is assigned to a combination band, i.e., the upper state is the upper state of the 1492-cm−1 band combined with ν1. Molecular parameters of the upper states responsible for the 2518- and 2585-cm−1 bands are determined by fixing ground state parameters to those already published.

Millimeter-wave spectrum of the CCO radical

The pure rotational spectrum of the CCO radical in the /sup 3/..sigma../sup -/ ground electronic state has been observed in the laboratory in the region 45-185 GHz. The radical was generated in a 3.5 m long free space absorption cell by a DC glow discharge in carbon suboxide (C/sub 3/O/sub 2/). Seven rotational transitions of Nn = 2reverse arrow1 to 8reverse arrow7 in each triplet sublevels were precisely measured and the observed frequencies were least-squares analyzed to obtain molecular constants.

Infrared diode laser spectroscopy of the LiO radical

The fundamental vibrational band of the 7LiO radical in the ground electronic state Xu20092Πi was observed in a region from 720 to 850 cm−1 using a source frequency modulation infrared diode laser spectrometer. Radicals were generated in a high‐temperature cell by the reaction of lithium metal vapor with nitrous oxide. The observed spectrum was analyzed together with the radio‐frequency and microwave spectra already reported. It was found that the vibration‐rotation Hamiltonian employed in a previous paper was insufficient to fit all of the observed spectra simultaneously. The Hamiltonian was thus extended to include higher‐order corrections for the centrifugal distortion and Λ‐type doubling terms, and was used to derive molecular parameters.

Triple resonance for a three-level system of a chiral molecule

A new spectroscopic method of triple resonance is proposed for studying chirality of a molecule of C1 symmetry. Each enantiomer of such a molecule is of mixed parity and thus exhibits all three a-, b-, and c-types of rotational spectra. The present study concludes, by using time-dependent perturbation theory, that the transition probability between two of the three rotational levels under triple resonance differs for different enantiomer. This result can thus be of some significance for enantiomer differentiation.

Laboratory millimeter-wave spectrum of iron monoxide, FeO

Observation en laboratoire du spectre rotationnel pur de FeO dans letat electronique de base 5 Δi dans les regions autour de 154 GHz et 184 GHz