Chikashi Yamada

Diode laser study of the ν2 band of the methyl radical

The v2 = 1←0, 2←1, and 3←2 bands of the methyl radical were observed in the gas phase by infrared tunable diode laser spectroscopy at 606.4531, 681.6369, and 731.0757 cm−1. The observed vibration–rotation spectra were analyzed to derive precise values for the rotational constants, centrifugal distortion constants, and spin–rotation interaction constants. The absence of N = odd, K = 0 levels in the v2 = even states and of N = even, K = 0 levels in the v2 = odd states was confirmed, indicating that each vibrational state is nondegenerate. The observed band origins, when analyzed, led to a potential function for the out‐of‐plane bending vibration that has no potential hump at the planar configuration. The large negative anharmonicity of this potential was ascribed to a vibronic interaction with excited electronic states. The methyl radical was generated by a 60 Hz discharge in di‐tert‐butyl peroxide and was found to have a lifetime of about 1.4 msec; its concentration in the absorption cell was estimated to ...

Difference frequency laser spectroscopy of the ν1 band of the HO2 radical

The ν1 (O–H stretching) band of the HO2 radical was observed in absorption by using a difference frequency output obtained from an Ar ion laser and a cw dye laser as a source, combined with a multiple‐reflection discharge cell. Zeeman modulation was employed to improve the sensitivity. The HO2 radical was generated directly in the cell by a dc discharge in a mixture of allyl alcohol and oxygen. About 280 lines were observed and analyzed to precisely determine the rotational constants, centrifugal distortion constants, and spin‐rotation interaction constants in the ν1=1 state. The band origin was determined to be 3436.1951(4) cm−1, which is 22 cm−1 higher than the value previously obtained by a matrix isolation study.

Infrared diode laser spectroscopy of the CF3 ν3 band

The ν3 degenerate C–F stretching vibration–rotation band of the trifluoromethyl radical was observed in the gas phase by infrared diode laser spectroscopy and was analyzed to determine precisely the rotational constants, centrifugal distortion constants, and the band origin. The spectrum was found to be perturbed by the so‐called Δl,ΔK=2,2 and 2,‐1 interactions, and an analysis of the perturbation yielded the C0 rotational constant which was otherwise difficult to determine. The two r0 structure parameters, the C–F distance and the F–C–F angle, were calculated from the observed B0 and C0 rotational constants to be 1.318±0.002 A and 110.76±0.4°, respectively, where the errors were entirely due to the uncertainties of B0 and C0. A general quadratic force field was derived using the fundamental frequencies of 12CF3 and 13CF3 and also the ζ3 Coriolis coupling constant obtained by the present work. The observed vibration–rotation constants α3B and α3C were used to estimate two cubic potential constants φ133 an...

Diode laser spectroscopy of the BO2 radical vibronic interaction between the à 2Π u and [Xtilde] 2Π g states

The v 3 fundamental and accompanying hot bands of BO2 in the ground electronic state have been observed by a tunable infrared diode laser spectrometer and analysed to yield molecular constants of high precision in the ground, v 3, 2v 3, v 2, and v 2 + v 3 states. The anomalously low fundamental frequency [1278·2585 (4) cm-1] and the large, negative anharmonicity of the v 3 fundamental band are accounted for by a vibronic interaction between [Xtilde] 2Π g and A 2Π u through the v 3 vibration. The observation that the effective B constant is larger in the μ 2Σ than in the κ 2Σ states within the manifold of the v 2 state is explained by higher-order vibration-rotation and Renner-Teller interactions. The analysis leads to a determination of the W 2 parameter of Hougen, 3·87 ± 0·37 cm-1.

Diode laser spectroscopy of the CCl radical

Abstract Vibration-rotation transitions of the fundamental band have been observed for both C35Cl and C37Cl in the 2 Π 1 2 and 2 Π 3 2 states by using an infrared diode laser spectrometer with Zeeman modulation. A few lines of the “hot” band (v = 2 ← 1) have also been recorded for C35Cl. From an analysis of the observed spectra improved values were obtained for the vibrational harmonic frequency and anharmonicity constant, rotational constants, and Λ-doubling parameters. It was found necessary to take into account centrifugal distortion effects on the spin-orbit coupling constant A in the analysis, which gave ( dA dr ) e r e to be −176 ± 38 or −125 ± 38 cm−1, depending upon whether 2Σ− or 2Σ+ states contribute more to the Λ-type doubling. The equilibrium internuclear distance re was calculated from the derived rotational constants to be 1.64506 ± 0.00016 A.

Laser Stark and laser microwave double-resonance spectroscopy of deuterated fluoroacetylene with the CO2 laser

Abstract The CO 2 laser Stark spectrum of deuterated fluoroacetylene was identified with the aid of the double-resonance technique for the ν 3 , ν 3 + ν 5 − ν 5 , ν 3 + ν 4 − ν 4 , ν 3 + 2 ν 5 − 2 ν 5 , and ν 3 + ν 4 + ν 5 − ν 4 − ν 5 vibrational bands. Laser microwave double-resonance signals were observed in the presence of the Stark field. From the analysis of the double-resonance signals precise values of the dipole moment were obtained for 10 vibrational states, in Debye, with the uncertainties in parentheses: ground, 0.73292(22); ν 5 , 0.75656(17); ν 4 , 0.68412(24); 2 ν 5 (Σ + ), 0.78063(21); ν 4 + ν 5 (Σ + or Σ − ), 0.70698(19); ν 3 , 0.75772(30); ν 3 + ν 5 , 0.78270(18); ν 3 + ν 4 , 0.70822(17); ν 3 + 2 ν 5 (Σ + ), 0.80808(25); ν 3 + ν 4 + ν 5 (Σ + or Σ − ), 0.73329(17). The band origins were determined (in cm −1 ); ν 3 , 1045.9242(8); ν 3 + ν 5 − ν 5 , 1049.6441(8); ν 3 + ν 4 − ν 4 , 1047.8700(8); ν 3 + 2 ν 5 − 2 ν 5 (Σ + -Σ + ), 1053.0374(8); ν 3 + ν 4 + ν 5 − ν 4 − ν 5 (Σ + −Σ + or Σ − −Σ − ), 1051.5040(8).

Infrared diode laser spectroscopy of the CF radical

Abstract The fundamental bands of the CF radical in the X 2 Π 1 2 and X 2 Π 3 2 electronic states were observed by using an infrared tunable diode laser as a source. Zeeman modulation could be used in detecting lines not only in the 2 Π 3 2 state, but also in 2 Π 1 2 , because the CF radical deviates considerably from Hunds case ( a ). From the least-squares analysis of the observed spectra, the following molecular constants were obtained: B e = 1.416 704 (37) cm −1 , α e = 0.018 419 (50) cm −1 , r e = 1.271 977 (17) A , D e = 6.68 (15) × 10 −6 cm −1 , p 0 = 0.008 580 (21) cm −1 , p 1 = 0.008 52 (11) cm −1 , and ν 0 = 1286.1281 (5) cm −1 , with three standard errors in parentheses.

Intramolecular motions and molecular structure of the CH3 radical

Abstract A normal coordinate analysis was carried out for the CH 3 radical to calculate the inertia defects and the centrifugal distortion constants. The calculated values were in fair agreement with the experimental results on the ν 2 band recently obtained by infrared diode laser spectroscopy. Third-order anharmonic potential constants were estimated to calculate vibration-rotation interaction constants and the equilibrium CH bond length. The conventional vibration-rotation interaction theory was extended to assess the effects of the large negative anharmonicity of the ν 2 mode on molecular parameters obtained from the observed spectra. The v 2 dependence of the C rotational constant was discussed by this treatment.

Diode laser spectroscopy of the SF radical

Abstract The vibration-rotation spectra of the SF radical were observed by an infrared diode laser spectrometer. The SF radical was generated directly in a cell by glow discharge in a mixture of carbonyl sulfide and carbon tetrafluoride. Zeeman modulation and discharge current modulation were employed to discriminate SF lines from many lines of the reactants and other products. Thirty two lines were assigned to the v = 1 ← 0 and 2 ← 1 bands of both 2 Π 1 2 and 2 Π 3 2 spin states. A least-squares analysis of all the assigned lines provided precise values for molecular parameters in v = 1 and 2 and the two band origins, where ground-state constants were constrained to microwave results. The harmonic frequency ω e was thus determined to be 837.6418(13) cm −1 , and the equilibrium bond length r e was calculated from the B e rotational constant to be 1.596 244(22) A with the error in parentheses, which included 2.5 standard deviations and the uncertainty of Plancks constant.

Infrared diode laser spectroscopy of FCO: The ν1 and ν2 bands

Abstract The ν1 (CO stretching) and ν2 (CF stretching) bands of the FCO radical were observed with Doppler-limited resolution by an infrared diode laser spectrometer with Zeeman and source modulation. The FCO radical was generated by a 60-Hz discharge in one of the following three gas mixtures: O2 + C2F4, CO + SF6, and CO + C2F4, all diluted with He. The observed spectra were analyzed to determine the rotational constants, the centrifugal distortion constants, and the spin-rotation interaction constants. The band origins, 1861.6372(1) and 1026.1283(1) cm−1 [with standard errors in parentheses], which were obtained, were found to agree well with matrix data, 1857 and 1023 cm−1, respectively. The assignment of the observed spectra to the FCO radical was further supported by observing the ν1 band of F13CO, which was obtained from 13CO and SF6. The molecular structure and the force field of FCO are briefly discussed by using molecular constants obtained from the observed spectra.