Yasuhiro Ohshima

Free-jet infrared absorption spectroscopy of the (N2O)2 van der Waals complex in the 8 μm region

Abstract The vibration-rotation spectrum of (N 2 O) 2 has been studied in the monomer ν 1 region (≈ 1280 cm −1 ) by free-jet absorption spectroscopy. The rotational constants determined are consistent with the centrosymmetric slipped parallel structure reported recently by Huang and Miller and by Howard. The band origin, 1279.7107 (6) cm −1 , is red-shifted from that of the monomer by 5.1926(6) cm −1 .

Mode‐specific infrared photodissociation of nitric oxide dimers: High‐resolution infrared spectroscopy of (14NO)2 and (15NO)2

The high‐resolution infrared absorption spectra of the symmetric (ν1) and the antisymmetric NO stretching (ν4) bands of nitric oxide dimer (NO)2 have been measured for 14NO and 15NO in supersonic free jets. The ν1 and ν4 bands exhibit a dramatic difference in linewidth: approximately 200 MHz [full width at half‐maximum (FWHM)] for the ν1 band and approximately 5 GHz (FWHM) for the ν4 band. The predissociation lifetimes deduced from the linewidths are in excellent agreement with those reported in the recent time‐resolved measurement for 14NO [Casassa et al., J. Chem. Phys. 89, 1966 (1988)]. There is no systematic dependence of the linewidth on the rotational states of (NO)2. Isotope substitution does not influence the linewidths significantly. However, the ν4 band structure of (15NO)2 is very different from that of (14NO)2, a difference that may be explained by a perturbation from a low‐lying singlet vibronic state. All of the experimental results obtained to date may be accounted for if it is assumed that...

Detection of HNCCC in TMC-1

The HNCCC molecule, an isomer of cyanoacetylene HCCCN, has been identified in TMC-1 through the observations with the Nobeyama 45 m telescope, considering the observed spectral pattern, results of ab initio calculations, and laboratory microwave spectroscopy. The column density of HNCCC in TMC-1 has been determined to be 3.8(0.6)×10 11 cm −2 , which is 160-450 times smaller than that of HCCCN

Vibrational and rotational structure and excited-state dynamics of pyrene

Vibrational level structure in the S(0) (1)A(g) and S(1) (1)B(3u) states of pyrene was investigated through analysis of fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation in a supersonic jet and through referring to the results of ab initio theoretical calculation. The vibrational energies are very similar in the both states. We found broad spectral feature in the dispersed fluorescence spectrum for single vibronic level excitation with an excess energy of 730 cm(-1). This indicates that intramolecular vibrational redistribution efficiently occurs at small amounts of excess energy in the S(1) (1)B(3u) state of pyrene. We have also observed a rotationally resolved ultrahigh-resolution spectrum of the 0(0) (0) band. Rotational constants have been determined and it has been shown that the pyrene molecule is planar in both the S(0) and S(1) states, and that its geometrical structure does not change significantly upon electronic excitation. Broadening of rotational lines with the magnetic field by the Zeeman splitting of M(J) levels was very small, indicating that intersystem crossing to the triplet state is minimal. The long fluorescence lifetime indicates that internal conversion to the S(0) state is also slow. We conclude that the similarity of pyrenes molecular structure and potential energy curve in its S(0) and S(1) states is the main cause of the slow radiationless transitions.

Coherent rotational excitation by intense nonresonant laser fields

The rotation of molecules in the gas phase can be coherently excited by irradiation with strong nonresonant short laser pulses, interacting with the molecular anisotropic polarisability. Such coherent rotational excitation has been attracting much attention because of the intriguing nature of the rotational wave packet thus created, and its wide applicability to dynamical studies and advanced optics. In this review article, we first survey various experimental schemes adopted so far for externally controlling molecular rotation, and then describe a new approach based on a quantum-state resolved spectroscopic probe for investigating coherent rotational excitation by intense nonresonant laser fields. Representative examples are given to show how the method provides detailed information on excitation pathways in wave-packet creation, and how it realises full quantum-state reconstruction of the rotational wave packet in a favourable case. We also describe an advanced wave-packet control, i.e. the creation and characterisation of a unidirectionally rotating wave packet, and discuss a further extension of this approach to explore coherent vibrational excitation.

Measurement of inclusive particle spectra and test of MLLA prediction in e+e− annihilation at s=58Gev

Abstract Inclusive momentum spectra are measured for all charged particles and for each of π ± , K ± , K 0 K 0 , and p p in hadronic events produced via e + e − annihilation at s =58 Gev . The measured spectra are compared with QCD predictions based on the modified leading log approximation (MLLA). The MLLA model reproduces the measured spectra well. The energy dependence of the peak positions of the spectra is studied by comparing the measurements with those at other energies. The energy dependence is also well described by the MLLA model.

Laboratory detection of C5S by pulsed-discharge-nozzle Fourier transform microwave spectroscopy

The rotational spectrum of C 5 S in the X 1 Σ + (υ=0) ground state has been observed for the first time using a Fabry-Perot-type Fourier transform microwave spectrometer combined with a pulsed discharge nozzle. C 5 S was generated by a discharge in a mixture of CS 2 and C 2 H 2 diluted in Ar, and subsequently cooled down to a few kelvins in a supersonic jet. Eight rotational transitions of C 5 32 S have been observed in the 5-20 GHz region. Three lines for the less abundant 34 S species have also been detected to confirm the carrier of the observed lines to be C 5 S

Laboratory detection of HC9N using a Fourier transform microwave spectrometer

The laboratory microwave spectrum of a linear carbon chain molecule, HC9N (cyano-octatetra-yne), has been observed for the first time by discharging a mixture of vinylcyanide and acetylene diluted in argon. The absorption spectrum was observed in a supersonic beam, using a pulsed-nozzle Fabry-Perot-type Fourier transform microwave spectrometer. Frequencies of 11 rotational transitions have been combined with the previously reported astronomical data, yielding accurate ground state parameters, B0 = 290.518322(57) MHz and D0 = 0.874(78) Hz. 8 refs.

Infrared–microwave double resonance and diode laser spectroscopy of the ν2/ν4 bands of SnH4

The interacting ν1 and ν3 bands of SnH4 have been studied by infrared absorption and infrared‐microwave double resonance spectroscopy. The infrared spectrum has been taken with Doppler‐limited resolution using a tunable diode laser. Pure rotational transitions within the ν3 state and rovibrational transitions between the ν1 and ν3 state have been observed by infrared‐microwave double resonance. The infrared and microwave data have been fitted simultaneously to the ν1 and ν3 Hamiltonian coupled by one vibration–rotation interaction term. Seventeen spectroscopic constants have been determined for each of the five most abundant isotopic species.

Free-jet infrared absorption spectroscopy of rare gas-11BF3 complexes in the 7 μm region

High‐resolution infrared absorption spectra of the van der Waals complexes of BF3 with a rare gas atom (Ne, Ar, and Kr) are obtained near the ν3 band of BF3 monomer in a supersonic free jet. Each spectrum shows a characteristic perpendicular band of a symmetric‐top molecule with C3v symmetry. The bands are shifted toward the red with respect to the monomer band by 0.3933(4), 1.7609(1), and 2.4059(4) cm−1 for NeBF3, ArBF3, and KrBF3, respectively. The Coriolis coupling constants of the complexes are almost identical to that of the monomer. These results show that complexing with a rare gas atom does not strongly influence the ν3 vibrational motion in BF3. The observed red shifts correlate well with the polarizabilities of the rare gas atoms. This finding is explained in terms of the instantaneous dipole–induced dipole interaction. The observed full widths of the Doppler‐limited spectral lines, typically 70 MHz, indicate that the lower limit of the vibrational predissociation lifetime is 2 ns.