Koichi M.T. Yamada

Infrared spectra of water clusters in krypton and xenon matrices

The infrared absorption spectra of the water molecules and small water clusters, (H(2)O)(n) with n = 2-6, trapped in solid argon, krypton, and xenon matrices have been investigated. The infrared bands of the water clusters with n = 5 and 6 in krypton and n = 3, 4, 5, and 6 in xenon matrices have been identified for the first time in the bonded OH stretching region. The frequency shifts in the bonded OH stretching band of the water dimer and trimer in xenon matrices show fairly large deviations to the red from the empirical correlation between the matrix shifts and the square root of the critical temperatures of the matrix material. The observed anomalous shifts suggest that the water dimer and trimer in solid xenon are trapped in multiple sites, and that the structures of the preferential trapping sites are different from those in argon and krypton matrices.

Experimental ground-state combination differences of CH5+

High-resolution spectroscopy helps to elucidate the highly dynamic structure of protonated methane. [Also see Perspective by Oka] Getting a handle on the CH5+ spectrum Protonated methane, CH5+, fascinates chemists because it seems to break the rules. Theres no obvious place for the fifth hydrogen to bind, and so what happens is that all five hydrogens shuffle about like participants in an endless round of a musical-chairs game. And yet, the molecule has a vibrational spectrum that suggests some semblance of tighter ordering. Asvany et al. have now measured high-resolution vibrational spectra at two low temperatures (10 and 4 Kelvin). Their accompanying analysis makes headway on assigning the peaks and enhancing understanding of the molecules dynamic structure. Science, this issue p. 1346 Protonation of methane (CH4), a rather rigid molecule well described by quantum mechanics, produces CH5+, a prototypical floppy molecule that has eluded definitive spectroscopic description. Experimental measurement of high-resolution spectra of pure CH5+ samples poses a formidable challenge. By applying two types of action spectroscopy predicated on photoinduced reaction with CO2 and photoinhibition of helium cluster growth, we obtained low-temperature, high-resolution spectra of mass-selected CH5+. On the basis of the very high accuracy of the line positions, we determined a spectrum of combination differences. Analysis of this spectrum enabled derivation of equally accurate ground state–level schemes of the corresponding nuclear spin isomers of CH5+, as well as tentative quantum number assignment of this enfant terrible of molecular spectroscopy.

Infrared spectra of the (H2O)n-SO2 complexes in argon matrices

The infrared spectra of the (H(2)O)n-SO(2) complexes trapped in argon matrices have been investigated using Fourier transform infrared spectroscopy. In addition to the 1:1 and 2:1 complexes, the first spectroscopic evidence for the 3:1 complex has been obtained from the spectra of the SO stretching and the OH stretching modes. The observed frequency shifts in the bonded OH stretching region indicate that the hydrogen bonds of the 2:1 and 3:1 complexes are strengthened compared to that of the 1:1 complex, which suggests the cyclic structure of the complexes.

Infrared Spectra of Carbon Monoxide in Kr and Xe Matrices: Shifts of the Vibrational Line Positions

The infrared spectra of CO in Kr and Xe matrices have been measured with an improved resolution. On the basis of the concentration and temperature dependence, fine structures in the CO stretching fundamental band have been assigned to the CO monomer and the dimer. The red shifts of the vibrational line position of CO observed in the Ar, Kr, and Xe matrix increase monotonically with this order. The splitting of the fine structure decreases with this order.

High resolution infrared spectra of the linear carbon cluster C7: The ν4 stretching fundamental band and associated hot bands

High resolution infrared spectra of the nu(4) fundamental antisymmetric stretching mode and associated hot bands of the linear carbon cluster C(7) were recorded using a tunable diode laser spectrometer in the frequency range of 2135-2141 cm(-1). Spectra of the nu(4) fundamental, nu(4)+nu(11)-nu(11), nu(4)+2nu(11)-2nu(11), and nu(4)+nu(8)-nu(8), bands have been analyzed and are compared to recent experimental results and high level ab initio calculations. In particular, the presented results give experimental evidence for the rigidity of C(7) and confirm theoretical predictions of a rather regular chain molecule, similar to the cases of C(4), C(5), and C(9). For the two energetically low-lying bending modes, nu(8) and nu(11), the rotational constants differ by less than 0.2%, from the ground state value, B(0)=0.030 624 4(28) cm(-1), in good agreement with the recent calculations by Botschwina [Chem. Phys. Lett. 354, 148 (2002)]. From the hot band analysis and the [script-l]-type doubling constant q, experimental values for the band origins of the nu(8) and nu(11) fundamentals have been derived.

Absorption line profiles of N2O measured for the J = 25-24 and 26-25 rotational transitions

Abstract The self- and foreign (Ar, N 2 , and O 2 )-pressure effects on the submillimeter-wave absorption line profiles have been investigated for the J =26–25 and 25–24 rotational transitions of N 2 O using the AIST terahertz spectrometer. By fitting the observed absorption profiles with the Galatry functions, the integral intensity, line-center position, Lorentzian width and contraction parameter were determined for each absorption line. The obtained pressure-broadening coefficients are consistent with the literature values reported for infrared spectra. The pressure dependence of contraction parameter was determined for the self-effect. The line shifts were found to be small.

Infrared spectra of the water-nitrogen complexes (H2O)2–(N2)n(n=1–4) in argon matrices

The infrared spectra of the water-nitrogen complexes trapped in argon matrices have been studied with Fourier transform infrared absorption spectroscopy. The absorption lines of the H20-N2 1:1, 1:2, 1:n, and 2:1 complexes have been confirmed on the basis of the concentration effects. In addition, we have observed a few lines and propose the assignments for the 2:2, 2:3, and 2:4 complexes in the nu1 symmetric stretching and nu2 bending regions of the proton-acceptor molecule, and in the bonded OH stretching region of the proton-donor molecule. The redshifts in the bonded OH stretching mode and blueshifts in the OH bending mode suggest that the hydrogen bonds in the (H2O)2-(N2)n complexes with n = 1-4 are strengthened by the cooperative effects compared to the pure H2O dimer. Two absorption bands due to the 3:n complexes are also observed near the bonded OH stretching region of the H2O trimer.

Spectroscopic identification of the CO-H2O 2-1 cluster trapped in an argon matrix

The infrared spectra of the carbon monoxide-water cluster as well as the CO monomer and dimer in an argon matrix at cryogenic temperatures have been reinvestigated on the basis of the isotope substitution experiment with 12CO and 13CO. Lines due to the CO-H2O 2-1 cluster in the matrix have been unambiguously identified in the CO and OH stretching regions. The isotope effect on the vibrational frequency of the cluster is observed in the CO stretching vibration but neither in the symmetric nor antisymmetric OH stretching vibrations. Each of the two vibrational lines due to the two CO vibrations of the CO-H2O 2-1 cluster is examined by comparing the expected spectral features at a 12CO/13CO ratio on a simulation with those observed experimentally. The migration of the trapped molecules (CO and H2O) in the matrix is discussed, in which the observed spectral change with the deposition temperature from 14 K to 30 K is explained.

Lowest bending mode of 13C-substituted C3 and an experimentally derived structure

The ν2 lowest bending mode of linear C3 and of all its 13C-substituted isotopologues was recorded using a terahertz-supersonic jet spectrometer in combination with a laser ablation source. Sixty-five ro-vibrational transitions between 1.8 and 1.9 THz have been assigned to linear C12C12C12, C12C12C13, C12C13C12, C13C13C12, C13C12C13, and C13C13C13. For each isotopologue, molecular parameters were obtained and the C-C-bond length was derived experimentally. All results are in excellent agreement with recent ab initio calculations [B. Schröder and P. Sebald, J. Chem. Phys. 144, 044307 (2016)]. The new measurements explain why the interstellar search for singly substituted C12C12C13 has failed so far. A spectral line list with recommended transition frequencies based on global data fits is given to foster future interstellar detections.

Correlation diagrams between the free-rotor and the hindered rotor states of a diatomic molecule: energy levels and transition moments obtained by numerical integration of the schrödinger equation

We present a numerical technique for the direct calculation of the rotational eigenvalues and transition moments of a rigid diatomic 1Σ rotor in an external axially-symmetric potential. Because this technique does not require an expansion in spherical harmonics, the wavefunctions and energy eigenvalues are obtained without having to perform integrals over the potential energy function, or having to calculate (and truncate) a Hamiltonian matrix. We use our technique to show the effect of the external field on the molecular spectra and present correlation diagrams of energy levels and transition moments between high barrier and free-rotor limits. The case of double minima potential energy functions, including those with inequivalent minima, is presented. The general features of the rotational states and transition probabilities of rotors in such potential energy functions is explored to serve as a guide for future experimental work. The presentation of the technique and of the intricacies of the energy levels and transition moments of the double minima potential energy functions is intentionally pedagogical.