Takayoshi Amano

Microwave spectrum of the molecular oxygen in the excited vibrational state

Abstract The fine-structure spectra of 16O2 in the first excited vibrational state have been observed at room temperature with a double-modulation spectrometer. The spectra of an isotopic species 16O18O in the ground state are also observed in natural isotopic abundance. Revised energy formulas, which are derived as a slight extension of Tinkham and Strandbergs treatment, are used in the analyses, and much more accurate equilibrium molecular constants are determined; λ′e = 59 429.08 ± 0.11 MHz, μe = −252.265 ± 0.011 MHz, Be = 43 336.2 ± 1.5 MHz, and r e = 1.20748 ± 0.00005 A .

Hyperfine interactions and Λ-type doubling in the microwave spectrum of the NS radical

Abstract Strong absorption lines due to free NS radicals have been observed by means of Stark modulated microwave spectrometers, in the discharge products of a mixture of nitrogen and sulfur dichloride or sulfur monochloride. The rotational transitions J = 3 2 ← 1 2 in the 2 Π 1 2 state as well as J = 5 2 ← 3 2 both in the 2 Π 1 2 and 2 Π 3 2 states are analyzed to investigate the Λ-type doubling and the hyperfine interactions in two isotopic species 14 N 32 S and 14 N 34 S. The parity considerations lead to negative sign of the Λ-type doubling parameter α p , which indicates that the dominant perturbing state is a 2 Σ − state not identified yet. Relative magnitudes of hyperfine constants of NS are very similar to those of NO, although their absolute values in the former are consistently smaller than in the latter. The rotational constant B 0 = 23156.01 ± 0.16 MHz obtained in the present analysis, combined with α e B from the γ-band analysis, gives an accurate equilibrium internuclear distance r e = 1.4938 ± 0.0002 A . The electric dipole moment is determined to be 1.81 ± 0.02 Debye in the 2 Π 1 2 state by the Stark effect measurements.

Microwave spectrum of the NCO radical

Abstract The rotational spectrum of the linear triatomic radical NCO has been observed by means of a Stark modulated microwave spectrometer. The NCO radical was produced by mixing HNCO with the products of a microwave discharge in CF 4 . The observed rotational transitions J = 5 2 ← 3 2 , and 7 2 ← 5 2 in the 2 Π 3 2 state and J = 5 2 ← 3 2 in the 2 Π 1 2 state have been analyzed by using Hougens formulation for a linear triatomic molecule in a 2 Π state. The rotational constant, the centrifugal distortion constant, the Λ-type doubling constant, the hyperfine constants and the dipole moment have been determined. Consideration of the Λ-type doubling constant leads to the conclusion that the upper electronic state perturbing the 2 Π state is A ( 2 Σ + ) .

High-resolution infrared and microwave spectroscopy of the ν4 and 2ν2 bands of 14NH3 and 15NH3

Abstract More than two thousand Stark resonances of the ν 4 and 2 ν 2 band transitions of 14 NH 3 and 15 NH 3 were observed at Doppler-limited resolution with a CO laser. Fourier transform infrared spectroscopy on 15 NH 3 is also carried out. Thirty-six new microwave transitions including seven perturbation-enhanced transitions are observed in the v 4 = 1 excited vibrational state of 14 NH 3 and 15 NH 3 . Accuracies of all available spectroscopic data on the v 4 = 1 and the v 2 = 2 states are evaluated and analyses of the vibration-rotation spectra are performed. The Coriolis interaction between the closely lying v 4 = 1 a (antisymmetric level) and v 2 = 2 s (symmetric level) states is explicitly included in the analysis. Smaller Coriolis interactions between the v 4 = 1 a and the v 2 = 1 s states and between the v 2 = 2 s and the v 2 = v 4 = 1 a states (i.e., ( v 1 , v 2 , v ′ 3 , v ′ 4 ) = (0 1 0 0 1 1 )) are also taken into consideration. The accuracy in determination of the principal molecular constants is 10 −6 . The parameters thus obtained reproduce the frequencies of the vibration-rotation transitions and inversion transitions within the accuracy of 0.0024 cm −1 .

Microwave spectrum of the ClO radical

Abstract Rotational transitions in the 2 Π 3 2 and 2 Π 1 2 electronic states have been investigated for both the 35ClO and 37ClO radicals by means of Stark modulated microwave spectrometers. Improved values were obtained for the rotational constants, Λ-doubling parameters and hyperfine constants of both radicals. It was found necessary to consider the effect of centrifugal distortion including the dependence of the spin-orbit coupling constant A on the internuclear distance. The distortion constant De was 0.077 ± 0.016 MHz and the value of A′ = (r dA dr ) at the equilibrium internuclear distance was 320 ± 60 cm−1, assuming a value for A determined from electron-paramagnetic-resonance data. The equilibrium internuclear distance re was calculated to be 1.569 ± 0.001 A from the rotational constants B0 for 35ClO and 37ClO. A detailed analysis of the second order Stark effect of the F = 0 ← 1 and F = 1 ← 1 components of the upper series of the J = 3 2 ← 1 2 rotational transition in the 2 Π 1 2 state of 35ClO was performed and the electric dipole moment was determined to be 1.239 ± 0.010 D. This value was confirmed for the 2 Π 3 2 state of 35ClO where the Stark effect is first-order for weak electric fields. (The indicated undertainties represent three times the standard errors of the reported values).

Infrared-microwave double resonance of 12CH3OH with a CO2 laser

Abstract The Stark effect of the 22 ← 21(E1), 21 ← 30(E1) microwave transitions in the ground state and the 22 ← 21(E1) microwave transition in the first excited CO stretching vibrational state are measured by means of infrared-microwave double resonance with the qQ1(2)E1 infrared transition as the pump transition in the range of 1000 to 2300 V/cm. The dipole moments μa and μb as well as the off-diagonal rotational constant Dab are determined for both the ground and the excited states. The frequency of the qQ1(2)E1 infrared transition is found to be lower by 128 ± 2 MHz than that of the P(34) CO2 laser.

High‐resolution laser spectroscopy of the ν3 vibration‐rotation band of HCOOH

The ν3 (C = O stretching) band of HCOOH has been studied by the techniques of CO laser Stark spectroscopy and tunable diode laser spectroscopy. The coincidence in frequency between the 13–12 P(15) CO laser line and the 110←211 transition of the ν3 band has been found by Stark spectroscopy and confirmed by laser‐microwave double resonance. It is found that the Ka = 4 and Ka = 7 levels of the ν3 state are perturbed because of Coriolis interactions with the close‐lying ν5+ν9 and ν6+ν9 states, respectively. The band origin, rotational and centrifugal distortion constants, and components of the dipole moment are determined for the ν3 state from the analysis of the unperturbed transitions. The Coriolis coupling constants and information on the interacting states are obtained from the analysis of perturbed transitions.

Infrared–microwave double resonance studies of collison‐induced transitions and energy transfer processes between vibration–rotation–inversion levels of NH3

When the 14NH3 molecules in the upper inversion level of the J=8, K=7 (para) rotational state are pumped by using the N2O P (13) laser line, many microwave inversion lines change their intensities because of collision‐induced populational transfer. Pressure dependence of this effect has been studied for several tens of inversion transitions in the ground vibrational state. The non‐Boltzmann distribution introduced into the pumped levels is transfered to other levels by two mechanisms: (i) collision‐induced transitions into or out of the pumped levels and succeeding cascading processes and (ii) selective energy transfer mechanisms to collision partners. In the former mechanism the transfer of populational change is caused by the transition of pumped molecules whereas in the latter it is caused by collision partners. Although the first mechanism is more efficient than the second, the second mechanism is not negligible and causes the populational change in also ortho rotational state. We used mixtures of 15N...

Microwave spectrum of 35ClO in the excited vibrational state and a comment on the centrifugal distortion constant

Abstract The J = 3 2 ← 1 2 transitions of 35 ClO in v = 1 of the 2 Π 1 2 state were measured and analyzed to obtain the following constants (in megahertz: B = 18 444.86 ± 0.18, p eff = 669.32 ± 1.08, a − (b + c) 2 = 157.05 ± 0.97 , d = 169.77 ± 0.99, and eqQ = − 84.78 ± 0.30. The equilibrium bond length is calculated to be 1.56954 ± 0.00005 A. The transitions in the ground vibrational state, which were reported previously, were reanalyzed by taking into account the matrix elements off diagonal in J of the hyperfine interactions, and led to a refined centrifugal distortion constant, 0.0476 ± 0.0154 MHz. The vibrational frequency increased accordingly to 782 ± 126 cm −1 , which agreed with the value 870 ± 90 cm −1 obtained from a relative-intensity measurement, and also with other optical spectroscopic data.

Collisional relaxation among rotational levels of NH3 studied by infrared-microwave double resonance

Abstract Double-resonance signals induced by molecular collisions are observed in 25 inversion transitions of NH 3 . It is found that the collision-induced transitions do not necessarily occur in accordance with the dipole-type selection rule reported previously.