Masaharu Fujitake

The millimeter‐ and submillimeter‐wave spectrum of dichlorocarbene CCl2: Electronic structure estimated from the nuclear quadrupole coupling constants

The pure rotational spectrum of CCl2 in the ground state was observed for the first time in the millimeter‐ and submillimeter‐wave region. The CCl2 molecule was generated directly in a free space cell by a dc glow discharge in CCl4 . Several transitions showed hyperfine splittings arising from the nuclear quadrupole coupling of two Cl atoms. Analysis of the observed spectrum yielded the rotational, centrifugal distortion, and nuclear quadrupole coupling constants of the C35 Cl2 species. The r 0 structure was derived from the rotational constants to be r 0 (C–Cl)=1.7157 A and θ0 (ClCCl)=109.2°. The ionic and π character of the C–Cl bond were estimated from the nuclear quadrupole coupling constants to be 0.26 and 0.32, respectively.

Detection of the NaO radical by microwave spectroscopy

The rotational spectrum of the NaO radical in the four lowest vibrational states was observed in the millimeter‐ and submillimeter‐wave region. The NaO radical was generated by the reaction of the sodium vapor with N2O directly in a high‐temperature absorption cell. Analysis of the observed spectra yielded the rotational and centrifugal distortion constants, Λ‐type doubling constants, spin–orbit interaction constants, and hyperfine interaction constants in the four vibrational states. The NaO radical is clearly shown to have the 2Πi ground electronic state with an anomalously large Λ‐type doubling constant and very small hyperfine interaction constants. The molecular constants derived are discussed in terms of the ionic character of the bond.

The microwave spectrum of the AlO radical

The rotational spectrum of the aluminum monoxide radical in the ground electronic state X 2Σ+ was observed in the millimeter‐ and submillimeter‐wave region. Aluminum monoxide radicals were generated directly in a flow reactor absorption cell by the reaction of N2O with aluminum vaporized from a high‐temperature crucible. The observed spectrum was analyzed to yield molecular constants including the rotational constant, centrifugal distortion constant, spin–rotation interaction constant, magnetic hyperfine interaction constants, and nuclear quadrupole coupling constant.

THE MICROWAVE SPECTRUM OF THE LiO RADICAL

The rotational spectra of the 7LiO radical in the v=0 and v=1 vibrational states were observed in the millimeter and submillimeter wave region. The LiO radical was generated by the reaction of lithium vapor with N2O directly in a high temperature absorption cell. The rotational and centrifugal distortion constants, Λ‐type doubling constants, spin–orbit interaction constant, and hyperfine interaction constants were derived through analysis of the rotational spectra observed in the present study combined with the radio frequency spectra of Λ‐type transitions reported by S. M. Freund et al. [J. Chem. Phys. 56, 1467 (1972)]. The LiO radical was confirmed to have a 2Πi ground electronic state with an exceptionally large Λ‐type doubling constant, as in the case of NaO. A pure precession hypothesis applied to the observed p Λ‐type doubling constant gives the Σ–Π energy difference to be 2565 cm−1.

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

We have analyzed the near-infrared band of NO3 observed at 7602 cm−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′′–X 2A2′ 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...

Development of millimeter- and submillimeterwave spectroscopy and its application to isotopically-substituted nonpolar molecules, deuterated cubane and deuterated cyclobutanes

Abstract A spectroscopic method has been developed to observe rotational spectra of molecules in the millimeter- and submillimeter-wave regions. Advantages and disadvantages of the method are discussed and compared to those of Stark-modulation and Fourier-transform spectroscopy in the centimeter-wave region. As examples of the methods applicability, the results for cubane-d and cis and trans cyclobutane-1,2-d 2 are presented. The transitions of J = 14 ← 13 up to 26 ← 25 are observed for cubane-d, yielding the rotational and centrifugal distortion constants B 0 = 3220.720 08 (85) and D JO = 0.000 180 99 (93) MHz; values in parentheses represent three standard deviations. Trans cyclobutane-1,2-d 2 is found to exist in an equatorial-equatorial and an axial-axial conformation, with only the b-dipole component being nonvanishing, as expected from previous results on the structure of cyclobutane. The observed spectra lead to the rotational constants A = 9 794.3831 (58), B = 9 758.3272(56), and C = 5 782.6540(73) and A = 9 738.242 (15), B = 9 693.452(14), and C = 6 048.564 (14) MHz, for the two forms, respectively; values in parentheses again represent three standard deviations. Cis cyclobutane-1,2-d 2 is expected to exist in two equivalent forms, axial-equatorial and equatorial-axial. The observed spectrum exhibits the effect of puckering. Preliminary values of the rotational constants are A = 9 938.757 (47), B = 9 577.008(47), and C = 5 913.212(41) MHz.

Microwave spectroscopic detection of dichlorosilylene SiCl2 in the ground state

The microwave spectrum of dichlorosilylene SiCl2 has been observed to characterize this molecule of chemical interest. The molecule was generated by the thermal reaction between silicon powder and tetrachlorosilane at about 1000 °C. The rotational constants and the centrifugal distortion constants were determined for the three isotopic species Si35Cl2, Si35Cl37Cl, and Si37Cl2. The nuclear quadrupole coupling constants were determined from triplet hyperfine splittings observed for several transitions. The asymmetry of the Cl nuclear quadrupole coupling tensor was found to be very large and was accounted for by π electron backdonation from Cl to Si.

Donor–acceptor interchange tunneling in HDO–DOH and the higher energy HDO–HOD isotopomer

The microwave and submillimeter spectra of the a‐type K=0←0 and K=1←1, c‐type K=1←0, and isotopically allowed b‐type K=1←0 bands of the O–D bonded HDO–DOH water dimer isotopomer and the higher energy O–H bonded HDO–HOD isotopomer have been measured using molecular‐beam electric resonance optothermal and pulsed‐nozzle Fourier‐transform microwave spectrometers. The present results obtained in He and He/Ne seeded molecular beams give the first evidence for the presence of the higher energy O–H bonded mixed protonated‐deuterated water dimers. These species were not reported previously in studies using seeded Ar molecular beams. The donor–acceptor interchange tunneling splittings are found to be 1322.1019(43) and 5004.059(20) MHz for the HDO–DOH and the metastable HDO–HOD dimers, respectively. For both isotopomers, the donor‐accepter interchange tunneling‐state selections rules for the b‐ and c‐type bands are consistent with tunneling pathways corresponding to geared partial internal rotation of the two subuni...

The microwave spectrum of dichlorosilylene (SiCl2) in excited vibrational states

Abstract The microwave spectrum of dichlorosilylene in excited vibrational states has been measured in the millimetre- and submillimetre-wave regions. Rotational and centrifugal distortion constants were determined for the ν 1 , ν 2 , 2ν 2 and ν 3 excited states of the Si 35 Cl 2 isotopic species and for the ν 2 and 2ν 2 states of Si 35 Cl 37 Cl. Analysis of the Coriolis resonance between the ν 1 and ν 3 states of Si 35 Cl 2 yielded values of the D Coriolis interaction constant with F constrained, of two higher-order terms and also an accurate value [5.402338(95) cm −1 ] of the energy difference between the two excited vibrational states. The rotational constants of Si 35 Cl 2 in the first excited states of the three normal vibrations were combined with those of the ground vibrational state reported in a previous paper [M. T animoto et al., J. Chem. Phys . 91 , 2102 (1989)] to obtain the equilibrium structure, harmonic and cubic/third-order anharmonic potential constants.

Submillimeter wave spectrum of the vibrationally induced rotational transitions of allene in the degenerate vibrational states

Abstract Vibrationally induced rotational transitions of allene in the degenerate vibrational states with the selection rules Δ k =0 and Δ l =±2 were measured in the submillimeter wave region. Six R-branch transitions were observed for the K =0 stack in each of the ν 9 , ν 10 and ν 11 states. Twelve transitions obeying the l =±1 ← ∓ 1 selection rules in the K =2 stack of the ν 10 state were also observed. The A 0 rotational constant in the ground vibrational state was determined to be 144259.8±3.5 MHz from an analysis of the present results, combined with those of a Fourier transform infrared study.