T. Amano

The dissociative recombination rate coefficients of H+3, HN+2, and HCO+

The dissociative recombination rate coefficients for H+3,u2009HN+2, and HCO+ are determined at 110, 210, and 273 K by monitoring the decay of the infrared absorption signals as a function of time. The rate coefficients are 1.8, 7.0, and 3.1 in units of 10−7 cm3u2009s−1 for H+3,u2009HN+2, and HCO+, respectively, at 273 K. These values agree very well with those obtained using the stationary afterglow or the merged beam techniques, but the values for H+3 disagree with that obtained by Smith and co‐workers (≤2×10−8 cm3u2009s−1) using the flowing afterglow/Langmuir probe method. The rate coefficients for H+3 and HCO+ disagree with theory which has predicted very slow dissociative recombinations in the lower vibrational states. The temperature dependences obtained here, although the temperature range is rather limited, are consistent with those obtained previously using the stationary afterglow (for H+3 and HCO+) and the merged beam (for HN+2) techniques. The measurements are extended to several vibration–rotation levels and ...

Diode laser spectroscopy of gas phase C5: the ν3 fundamental and associated hot bands

The spectrum of the linear carbon chain molecule C5 in the gas phase has been studied around 2170 cm−1, the region of the highest asymmetric stretching vibration ν3. The results were obtained using a tunable diode laser spectrometer and a cooled hollow cathode discharge in a flowing mixture of acetylene and helium. Four vibration–rotation bands were assigned and analyzed: the fundamental, a hot band arising from the v7=1, l=1 vibrational level, a second hot band arising from v7=2, l=0, and a third hot band tentatively ascribed to v5=1, l5=1. Small local perturbations were found to affect the upper vibrational states of two of the bands. Analysis of the data yielded accurate values for a number of molecular parameters for C5, e.g., the band origin ν3= 2169.4410(2) cm−1, the rotational constant, B0 =2557.63(9) MHz, and the l‐type doubling parameters, q7=3.99(6) MHz, and q5=2.36(9) MHz. The value of q7 may be used to estimate a value of 118 cm−1 for the lowest bending frequency of the molecule. There is no e...

Observation of the infrared absorption spectra of 20NeH+ and 22NeH+ with a difference frequency laser

The fundamental bands of 20NeH+ and 22NeH+ in the region around 3.7 μm have been observed in absorption. The wave numbers of 11 transitions of 20NeH+ and 8 transitions of 22NeH+ have been measured, from which we obtain the following molecular parameters (in cm−1, three standard deviations in parentheses): The equilibrium molecular constants B e , α e , D e , β e , ω e , ω e X e , and r e have also been derived.

Laboratory observation of the rotation-vibration spectrum of gas-phase C5

Abstract The highest asymmetric stretching fundamental (ν 3 ) of the gas-phase linear carbon chain C 5 has been detected in the laboratory using a cooled hollow-cathode discharge in C 2 H 2 +He or C 2 H 4 +He mixtures with a tunable diode laser spectrometer. Our work was guided by recent matrix-isolation and astronomical observations of this band. We have measured a total of 59 lines with J values ranging from 0 to 72. A small local perturbation is observed to affect upper-state energy levels around J ′=41. The measurements are analyzed to give accurate values of the band origin and the ground- and excited-state rotational parameters.

Infrared spectroscopy of NH+: An analysis of the perturbation between the X 2Π and a 4Σ− states

The v=1–0 vibration–rotation transitions in the Xu20092Π and au20094Σ− states as well as those between the two electronic states were observed with a difference frequency laser as a radiation source. The two electronic states (Xu20092Π and au20094Σ−) lie close together and interact each other strongly through the spin–orbit coupling. A merged least‐squares fit was carried out with the present infrared transition wave numbers, some of the previous optical term values, and the recent far‐infrared rotational transition frequencies to determine the spectroscopic parameters precisely. The equilibrium internuclear distance was obtained to be 1.0692±0.0002 and 1.0924±0.0001 A for the X and a states, respectively. The Λ‐type doubling transition frequencies were calculated for several of the lowest J states with the molecular constants obtained and the hyperfine coupling constants determined from the far‐infrared transitions.

Direct observation of the ν1 and ν3 fundamental bands of NH2 by difference frequency laser spectroscopy

Abstract The ν 1 and ν 3 bands of the NH 2 radical were detected in absorption in the 2.9- to 3.2-μm region using a tunable difference frequency laser and a long-path Zeeman-modulated discharge cell. About 100 rotation-vibration transitions were measured and a simultaneous analysis of the Coriolis-coupled ν 1 and ν 3 states was made. It was found that the ν 1 band is considerably stronger than ν 3 , in contrast to the similar molecule H 2 O. These results may prove useful in a search for interstellar NH 2 by means of its rotation-vibration spectrum.

Millimeter‐wave spectrum of NCS radical in the ground 2Π state

The rotational transitions of NCS have been observed in the 1 to 3 mm wavelength region in a hollow cathode discharge in a gas mixture of CS2 (∼1 mTorr) and N2 (∼30 mTorr). The molecular constants in the ground state are determined by fitting the observed frequencies to the standard Hamiltonian for 2Π states. The accuracy of the molecular constants are greatly improved compared with the values obtained from the optical data. The lines in the excited vibronic states have also been observed. The analysis including those excited state lines is in progress and the results will be published separately.

Observation of the v = 1 ← 0 band of SH (X2Π) with a difference frequency laser

Abstract The fundamental vibration-rotation band of SH (X2Π) has been studied in absorption at Doppler-limited resolution with an estimated accuracy of 0.002 cm−1. The band origin (ν0 = 2598.7675 ± 0.0003 cm−1) and the molecular constants for the excited vibrational state (v = 1), as well as improved molecular constants for the ground vibrational state, have been determined in a least-squares fit.

DIFFERENCE-FREQUENCY LASER SPECTROSCOPY OF GAS PHASE C2D IN THE 2800 CM-1 REGION

The gas phase C2D absorption spectrum has been studied in the 2800 cm−1 region using a high resolution difference‐frequency laser spectrometer. The C2D molecules were produced in a hollow cathode discharge in a mixture of C2H2 or C2D2 (∼20 mTorr) and D2 (∼400 mTorr). Two bands were identified and rotationally analyzed. One band at 2796 cm−1 was found to be a 2Π–2Σ+ transition with the lower state being the ground state. The upper level of this band is assigned to the (110) state in the ground electronic state, Xu20092Σ+. The other band at 2851 cm−1 is a 2Σ+–2Σ+ transition from the (001) state in Xu20092Σ+ to a vibronic 2Σ+ state which was found to be perturbed. Accurate molecular constants for the upper levels involved were determined from least‐squares fit. These constants as well as the observed transition frequencies are reported.

Difference frequency laser spectroscopy of HCNH+: Observation of the isotopic species and the hot bands

Author Institution: National Research Council of Canada, Herzberg Institute of Astrophysics; Department of Chemistry, Kyushu University