Kentarou Kawaguchi

HNC/HCN ratio in acetonitrile, formamide, and BrCN discharge.

Time-resolved Fourier transform (FT) spectrometry was used to study the dynamics of radical reactions forming the HCN and HNC isomers in pulsed glow discharges through vapors of BrCN, acetonitrile (CH(3)CN), and formamide (HCONH(2)). Stable gaseous products of discharge chemistry were analyzed by selected ion flow tube mass spectrometry (SIFT-MS). Ratios of concentrations of the HNC/HCN isomers obtained using known transition dipole moments of rovibrational cold bands v(1) were found to be in the range 2.2-3%. A kinetic model was used to assess the roles the radical chemistry and ion chemistry play in the formation of these two isomers. Exclusion of the radical reactions from the model resulted in a value of the HNC/HCN ratio 2 orders of magnitude lower than the experimental results, thus confirming their dominant role. The major process responsible for the formation of the HNC isomer is the reaction of the HCN isomer with the H atoms. The rate constant determined using the kinetic model from the present data for this reaction is 1.13 (±0.2) × 10(-13) cm(3) s(-1).

Low-excited f-, g- and h-states in Au, Ag and Cu observed by Fourier-transform infrared spectroscopy in the 1000?7500 cm?1 region

The infrared emission spectra of Au, Ag and Cu resulting from the laser ablation of metal targets in a vacuum were recorded using time-resolved Fourier-transform spectroscopy in the 1200–1600, 1900–3600, 4100–5000 and 5200–7500 cm−1 ranges with a resolution of 0.017 cm−1. The majority of the observed lines correspond to transitions between low-excited Rydberg (Nd10)nlj states of Cu (N = 3), Ag (N = 4) and Au (N = 5) with a principal quantum number n = 4, ..., 10; the most prominent lines being due to transitions between the states with high orbital momenta l = 3, ..., 5. This study reports 32 new lines of Au, 12 of Ag and 20 of Cu (with uncertainties of 0.0003–0.03 cm−1). From the lines observed here and in our previous works, we extract revised energy values for 85 energy levels (uncertainty 0.01–0.03 cm−1) of which eight levels of Au, three of Ag and four of Cu are reported for the first time. These newly reported levels have high orbital momentum l = 3, 4, 5.

Simultaneous analysis of the Ballik-Ramsay and Phillips systems of C2 and observation of forbidden transitions between singlet and triplet states.

6229 lines of the Ballik-Ramsay system (b(3)Σg (-)-a(3)Πu) and the Phillips system (A(1)Πu-X(1)Σg (+)) of C2 up to v = 8 and J = 76, which were taken from the literature or assigned in the present work, were analyzed simultaneously by least-squares fitting with 82 Dunham-like molecular parameters and spin-orbit interaction constants between the b(3)Σg (-) and X(1)Σg (+) states with a standard deviation of 0.0037 cm(-1) for the whole data set. As a result of the deperturbation analysis, the spin-orbit interaction constant AbX was determined as 6.333(7) cm(-1) and the energy difference between the X(1)Σg (+) and a(3)Πu states was determined as 720.008(2) cm(-1) for the potential minima or 613.650(3) cm(-1) for the v = 0 levels with Merer and Browns N(2) Hamiltonian for (3)Π states, which is about 3.3 cm(-1) larger than the previously determined value. Due to this sizable change, a new energy-level crossing was found at J = 2 for v = 3 (F1) of b(3)Σg (-) state and v = 6 of X(1)Σg (+) state, where the strong interaction causes a nearly complete mixing of the wave functions of the b(3)Σg (-) and X(1)Σg (+) states and the forbidden transitions become observable. Using the predictions of our deperturbation analysis, we were able to identify 16 forbidden transitions between the singlet and triplet states at the predicted frequencies with the expected intensities, which verifies our value for the energy difference between the X(1)Σg (+) and a(3)Πu states.

Time-resolved FTIR emission spectroscopy of Cu in the 1800{3800 cm -1 region: Transitions involving f and g states and oscillator strengths

Time-resolved Fourier-transform spectroscopy was applied to the study of the emission spectra of Cu vapours in a vacuum (10−2 Torr) produced in ablation of a Cu metal target by a high-repetition rate (1.0 kHz) pulsed nanosecond ArF laser (λ = 193 nm, output energy of 15 mJ). The time-resolved infrared emission spectrum of Cu was recorded in the 1800–3800 cm−1 spectral region with a resolution of 0.017 cm−1. The time profiles of the measured lines have maxima at 18–20 µs after a laser shot and display non-exponential decay with a decay time of 5–15 µs. This study reports 17 lines (uncertainty 0.0003–0.018 cm−1) of Cu I not previously observed. This results in seven newly-found levels and revised energy values for 11 known levels (uncertainty 0.01–0.03 cm−1). We also calculate transition probabilities and oscillator strengths for several transitions involving the reported Cu levels.

Spectroscopy of HF and HF-containing clusters in solid parahydrogen.

We report measurements of FT-IR absorption spectroscopy of HF, DF, and their clusters in solid parahydrogen (pH(2)). The observed spectra contain many absorption lines which were assigned to HF monomers, HF polymers, and clusters with other species, such as N(2), O(2), orthohydrogen (oH(2)), etc. The rotational constants of HF and DF monomers were determined from the cooperative transitions of the vibration of solid pH(2) and the rotation of HF and DF. Small reduction of the rotational constants indicates that HF and DF are nearly free rotors in solid pH(2). Time dependence of the spectra suggests that HF and DF monomers migrate in solid pH(2) and form larger polymers, probably via tunneling reactions through high energy barriers on inserting another monomer to the polymers. The line width of HF monomers in solid pH(2) was found to be 4 cm(-1), which is larger than that of other hydrogen halides in solid pH(2). This broad line width is explained by rapid rotational relaxation due to the accidental coincidence between the rotational energy of HF and the phonon energy with maximum density of states of solid pH(2) and the rotational-translational coupling in a trapping site.

THz rotational spectrum of H2F

In view of recent tremendous advance in astronomical observations in the submillimeter to THz region brought by the Herschel space craft, laboratory high-resolution spectroscopic investigations in that frequency region into unstable molecules, in particular, light hydride ions, are urgently needed. As a part of such endeavor, rotational transitions of H(2)F(+) were observed in the THz-region by using a tunable far-infrared spectrometer. These newly detected lines together with the submillimeter-wave lines obtained previously and the combination differences derived from infrared vibration-rotation lines were subject to a least-squares analysis that yielded a set of molecular constants with much better accuracy. The measured and predicted THz transition frequencies should prove to be a useful probe into detection of interstellar H(2)F(+).

Early negative ion studies related to C6H− and recent ion spectroscopy

Through a spectral line survey observation with Nobeyama 45-m radio telescope in the 28–50 GHz region toward a late type star IRC+10216, a series of lines of a linear molecule was found in 1995. The rotational constant was determined to be 1376.8641(43) MHz, and the molecule is called B1377. After the detection, various studies related this species were carried out, which are presented in this paper, including Aoki’s pioneering prediction and radio searches for NCO−, NCS−, and CCH−, etc. Finally, in 2006, McCarthy et al. succeeded in laboratory detection of the C6H− species by mm wave and FTMW spectroscopy and proved that the C6H− anion is B1377. We also report recent laboratory studies in the following topics:(1) time-resolved Fourier transform (FT) emission and absorption spectroscopy of molecular ions to obtain reaction rate constants, (2) FT infrared absorption spectrum of the H2F+ ion.