Nobukimi Ohashi

Group theoretical treatment of the planar internal rotation problem in (HF)2

Abstract The HF dimer is believed to exhibit an internal rotation tunneling process between two planar but nonlinear equilibrium configurations, during which tunneling the roles of the hydrogen-bonded and the free hydrogen atom are interchanged. This process can be represented schematically with labeled atoms as HlFaH2Fb ⇄ FaHlFbH2, and gives rise to a permutation-inversion group G4 containing four operations. In the present work the vibration-rotation-tunneling problem in (HF)2 is treated group theoretically in three ways: (i) by allowing tunneling only through a trans planar C2h intermediate, (ii) by allowing tunneling only through a cis planar C2v intermediate, and (iii) by considering the trans and cis tunneling processes both to occur, though not necessarily with the same probability. The molecular symmetry groups used for these treatments are (i) the point group C2h, (ii) the point group C2v, and (iii) a double group, which might be thought of as G 4 † = C 2h † = C 2v † . Nonplanar tunneling paths are not considered, since the internal axis method (IAM) coordinate system used here cannot easily be adapted to nonplanar internal rotation motions in this molecule. Various-details of energy level diagrams, symmetry species for operators, selection rules for spectroscopic transitions, and statistical weights are presented for the (HF)2 tunneling problem, as well as some speculation on the general question of when point groups, permutation-inversion groups, or double groups are preferable for treating large-amplitude vibrational motion problems.

Far-infrared spectrum and ground state constants of methyl amine

Abstract The far-infrared spectrum of methyl amine has been studied in the region 40 to 350 cm −1 by Fourier transform spectroscopy with an apodized resolution of 0.005 cm −1 or better. Both the pure rotational spectrum and the spectrum of the fundamental torsional band have been assigned. This paper reports the ground state constants obtained from a global fitting of a data set including ground state microwave transitions from the literature, as well as far-infrared pure rotational ground state transitions and ground state combination differences from the torsional band obtained in this work. Slightly over 1000 energy differences for the ground state with 0 ≦ K ≦ 19 and K ≦ J ≦ 30 were fit to 30 molecular parameters from a group theoretical formalism developed earlier, and a standard deviation of ±0.00063 cm −1 was obtained. An ambiguity (noted earlier in the microwave literature) in the determination of the structural parameter ϱ, which arises when two large amplitude motions are present in the molecule, can be understood and resolved using the present formalism.

Far‐infrared laser magnetic resonance detection and microwave spectroscopy of the PO2 radical

The PO radical has been detected by far‐infrared laser magnetic resonance (FIR LMR) using the CH3OH 369 μm and the CH3OD 305 μm laser lines as sources. The radical was generated by passing the microwave discharge products of H2O or of a H2/O2 mixture over powdered red phosphorus placed in an absorption cell. Subsequently, microwave spectroscopy was applied to observe low‐J transitions. The ground‐state molecular constants derived from the observed spectra are B=21 899.4915 (33), AeffJ=3.1026(30), D=0.031 120(42), p=188.01(51), qeff=−0.57(29), a=566.16(19), b=227.5(64), c=−415.3(64), and d=751.169(90), all in MHz with three standard errors in parentheses which apply to the last digits of the constants. The mechanism of the reaction generating PO is briefly discussed.

Microwave spectrum of methyl amine: Assignment and analysis of the first torsional state

Abstract The microwave absorption spectrum of methyl amine has been reinvestigated in the range from 7 to 90 GHz, with the aim of analyzing the first torsional state in more detail. By combining the newly obtained microwave data with the far-infrared and microwave data already available, it was possible to make and analysis of the tunneling-rotational levels of the first torsional state in which three types of Δ K = ±1 elements were introduced into the Hamiltonian matrix described in the group-theoretical formalism developed previously. The present global fit uses 38 molecular parameters (three fewer than previously) to describe 714 transitions involving tunneling-rotational levels of the first excited torsional state (57 more than previously). It resulted in a satisfactorily small standard deviation of 0.00095 cm −1 (almost the same as previously) for J ≦ 30 (five J values higher than included previously). On the basis of this fit, avoided crossings between K = 0 and 1 levels belonging to A and B species in the molecular symmetry group G 12 are discussed in detail for the first time. Stark effect data, remeasured during the present study, are also examined in connection with the Δ K = ±1 interaction.

Doppler-limited dye laser excitation spectroscopy of the DSO radical

Abstract The A 2 A′(003) ← X 2 A″(000) vibronic transition (16 370 to 16 425 cm −1 ) of the DSO radical in studied by Doppler-limited dye laser excitation spectroscopy. DSO is produced in a flow system by reacting the products of a microwave discharge in O 2 with D 2 S. About 637 observed lines are assigned to 987 transitions of the 19 subbands: K ′ a ← K ″ a = 6 ← 5, 5 ← 4, 4 ← 3, 3 ← 2, 2 ← 1, 1 ← 0, 0 ← 1, 1 ← 2, 2 ← 3, 3 ← 4, 0 ← 0, 1 ← 1, 2 ← 2, 3 ← 3, 4 ← 4, 3 ← 1, 2 ← 0, 0 ← 2, and 1 ← 3. They are analyzed to determine rotational constants, centrifugal distortion constants, and spin-rotation constants for both the ground and the excited electronic states. The band origin obtained is 16 413.874 (2.5σ = 0.002) cm −1 . The rotational constants determined are combined with the previous result on HSO (M. Kakimoto et al., J. Mol. Spectrosc. 80, 334–350 (1980)) to calculate the structural parameters for this radical in both the states: r( SO ) = 1.494(5) A , r( SH ) = 1.389(5) A , and ∠HSO = 106.6(5)° for the X 2 A″ state, and r( SO ) = 1.661(10) A , r( SH ) = 1.342(8) A , and ∠HSO = 95.7(21)° for the A 2 A′(003) state, where values in parentheses denote 2.5σ.

Far-infrared spectrum of methyl amine

Abstract The far-infrared spectrum of methyl amine has been studied in the 40- to 350-cm−1 region with a resolution of 0.005 cm−1 or better. The pure rotational spectrum in the first excited torsional state, as well as the fundamental torsional band, has been assigned. The data obtained have been combined with microwave data from the literature, and a global fit has been carried out, based on a group theoretical formalism developed previously. Over 650 transitions with 0 ≤ K ≤ 14 and K ≤ J ≤ 25 were fit to 41 molecular parameters, with a standard deviation of ±0.000 94 cm−1. This standard deviation was achieved by including J- and K-dependent (centrifugal distortion) corrections to the structural parameter ϱ. Problems remaining in the fit presumably arise from the neglect of five tunneling and nontunneling terms with selection rules ΔK = ±1. Some aspects of the torsional potential function and inversion potential function in this molecule are briefly discussed.

0.85 μm diode laser spectroscopy of 12C2H2

Abstract Five bands ( ν 1 + 2 ν 2 + ν 3 + 2 ν 4 0 , ν 1 + 3 ν 2 + 3 ν 4 1 + ν 5 1 , ν 2 + 3 ν 3 , 2 ν 2 + 2 ν 3 + ν 4 1 + ν 5 1 , and 2 ν 1 + ν 2 + ν 3 ) were restudied by means of near-infrared diode laser spectroscopy to obtain more precise upper state molecular constants. Intensity measurements were carried out for the four bands, ν 1 + 2 ν 2 + ν 3 + 2 ν 4 0 , ν 1 + 3 ν 2 + 3 ν 4 1 + ν 5 1 , ν 2 + 3 ν 3 , and 2 ν 1 + ν 2 + ν 3 , to obtain the transition band dipole moments. The latter values were found to be 1.42(27) × 10 −4 , 1.551(28) × 10 −4 , 2.474(35) × 10 −4 , and 1.067(22) × 10 −4 D, respectively, for each of the four bands.

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...

Far-infrared laser magnetic resonance spectra of the PH and PD radicals in X3Σ−

Abstract Far-infrared laser magnetic resonance (LMR) spectra of PD in the ground vibronic state ( X 3 Σ − , v = 0) were observed using the 570.6-, 380.6-, 287.3-, 232.9-, 191.6-, and 164.6-μm laser lines as sources, and the v = 1 spectrum was also observed with the 392.1-μm laser line. By combining the present results with mid-infrared LMR and optical spectroscopic data already reported, the molecular constants of PD in X 3 Σ − were refined as follows: B 0 = 4.362 8675(77), D 0 = 0.000 118 03(24), λ 0 = 2.208 48(57), γ 0 = −0.039 900(34), B 1 = 4.269 248(65), λ 1 = 2.209 5(10), γ 1 = −0.038 82(21), and ν 0 = 1653.284 91(51), all in cm −1 with 3σ in parentheses. The 31 P hyperfine coupling constants were determined to be α P = 0.004 330(39) and β P = −0.005 312(32) for the v = 0 state and α P = 0.004 66(40) and β P = −0.004 79(69) for the v = 1 state, again in cm −1 with 3σ in parentheses. The far-infrared LMR spectra of PH in the X 3 Σ − , v = 0 state were measured on five new laser lines, and an analysis of the observed spectrum combined with that already reported yielded molecular constants much improved in precision. Using the results on both PD and PH, the equilibrium structure and the potential constants up to the fourth order were derived, where allowance was made for adiabatic and nonadiabatic corrections: r e BO = 1.42140(22) A , ω e (PH) = 2366.79(16) cm −1 , a 1 = −2.3797(18), and a 2 = 3.461(14).

Fourier transform spectrum of the torsional band of hydrazine

Abstract The far-infrared torsional band of hydrazine has been studied by Fourier transform spectroscopy with an apodized resolution of 0.011 cm −1 . As a result of torsional as well as inversion tunneling, large splittings are observed in this b -type band. About 700 r R K and p P K transitions of 22 subbands with Δ K · K ″ from −10 to +11 were assigned. The A - B , B - A , and E - E transitions were assigned for all subbands except for the Δ K · K ″ = −2 and −1 subbands, for which only the nondegenerate transitions were observed. A global fitting, which includes all available ground state microwave data, was made using Hougens group theoretical formalism. Several fitting constants, i.e., B - C , the trans torsional tunneling constant h 3 v t , and the inversion tunneling constant h 5 v , were found to exhibit large changes upon torsional excitation. The values of these constants in the torsional fundamental state are: B - C = 184.52(30) MHz, h 3 v t = −912.0(21) MHz, and h 5 v = 1994.1(16) MHz, where the numbers in parentheses are 1 σ.