Study of infrared emission spectroscopy for the B(1)Δg-A(1)Πu and B'(1)Σg(+)-A(1)Πu systems of C2.

Thirteen bands for the B(1)Δg-A(1)Πu system and eleven bands for the B'(1)Σg(+)-A(1)Πu system of C2 were identified in the Fourier transform infrared emission spectra of hydrocarbon discharges. The B'(1)Σg(+)v = 4 and the B(1)Δg v = 6, 7, and 8 vibrational levels involved in nine bands were studied for the first time. A direct global analysis with Dunham parameters was carried out satisfactorily for the B(1)Δg-A(1)Πu system except for a small perturbation in the B(1)Δg v = 6 level. The calculated rovibrational term energies up to B(1)Δg v = 12 showed that the level crossing between the B(1)Δg and d(3)Πg states is responsible for many of the prominent perturbations in the Swan system observed previously. Nineteen forbidden transitions of the B(1)Δg-a(3)Πu transition were identified and the off-diagonal spin-orbit interaction constant AdB between d(3)Πg and B(1)Δg was derived as 8.3(1) cm(-1). For the B'(1)Σg(+)-A(1)Πu system, only individual band analyses for each vibrational level in the B'(1)Σg(+) state could be done satisfactorily and Dunham parameters obtained from these effective parameters showed that the anharmonic vibrational constant ωexe is anomalously small (nearly zero). Inspection of the RKR (Rydberg-Klein-Rees) potential curves for the B'(1)Σg(+) and X(1)Σg(+) states revealed that an avoided crossing or nearly avoided crossing may occur around 30,000 cm(-1), which is responsible for the anomalous molecular constants in these two states.

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 Brown's 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.

Low-lying electronic states in bismuth trimer Bi3 as revealed by laser-induced NIR emission spectroscopy in solid Ne.

Laser-induced near-infrared (NIR) emission spectra of neutral bismuth timer, Bi3, embedded in solid neon matrixes at 3 K were recorded in a range 870-1670 nm. Using photoexcitation with low energy photons at 1064 nm, two emission band systems were newly identified by their origin bands at T0 = 6600 and 8470 cm⁻¹. Accordingly, spectral assignment for three NIR emission band systems reported recently was partly revised for the one with its origin band at T0 = 7755 cm⁻¹ and reconfirmed for the others at T0 = 9625 and 11,395 cm⁻¹. Energy splitting by spin-orbit coupling between the pair of electronic energy levels in the ground state of bismuth trimer, Bi3, both having a totally symmetric vibrational mode of frequency at ω(e)" = 150 cm⁻¹, was determined to be 1870 ± 1.5 cm⁻¹. Transitions from the pair of electronically excited states, locating at T0 = 8470 and 9625 cm⁻¹ above the ground state and separated by spin­orbit coupling of 1155 cm⁻¹, have relatively long decay constants of τ ∼0.2 and ∼0.1 ms, respectively.

FTIR spectroscopy of NO3: perturbation analysis of the ν3+ν4 state.

High-resolution Fourier transform infrared spectra of the 15NO3 ν3+ν4 and ν3+ν4-ν4 bands were observed in the 1472 and 1112 cm(-1) regions. Compared with the case of 14N species, large effects of perturbations were recognized in many rotational levels of the 15NO3 ν3+ν4 state, and it was found that the ν2+2ν4 state is responsible for the perturbation. Although a direct Coriolis interaction (Δν2 = 1, Δν3(or Δν4)=1) is not present between these two vibrational levels, anharmonic terms including Φ344 and Φ444 mix ν3+ν4 and 3ν4, ν2+2ν4, and ν2+2ν4 mixes with ν2+ν4 to produce Coriolis interaction between ν3+ν4 and ν2+2ν4. An analysis gave the energy difference of 7.274 cm(-1) between two levels, and interaction parameters were determined. Similar perturbation analysis was applied for the 14N species, and the previous (p)P(N,K) assignment of the ν3+ν4 A'-ν4 E' band was changed for giving one A2' state. Spectral lines to another A1' state were not assigned because of weak intensity, which is explained by intensity anomaly through vibronic interaction, reflecting the transition moment of the B2E'-X2A2' electronic band.

Diffusion of hydrogen fluoride in solid parahydrogen.

We studied diffusion of hydrogen fluoride (HF) in solid parahydrogen (pH2) around 4 K. Diffusion rates were determined from time dependence of FT-IR spectra of HF monomers. The absorption of HF monomers shows temporal decay due to dimerization reaction via diffusion. It was found that the rates are affected by the sample temperature, the initial HF concentration, and annealing of samples. The observed non-Arrhenius-type temperature dependence suggests that the diffusion is dominated by a quantum tunneling process, that is, "quantum diffusion." Deceleration of the diffusion in condensed samples and acceleration in annealed samples were also observed. These results can be attributed to the fact that lower periodicity of samples due to impurities or defects suppresses the quantum tunneling. It seems to be difficult to explain the observed dependences by three possible diffusion mechanisms, exchange of chemical bonds, direct cyclic exchange, and exchange with mobile vacancy. Therefore, we propose a hypothetical mechanism by exchange of vacancies originating from quantum effect.

Rovibrational states of ClHCl- isotopologues up to high J: a joint theoretical and spectroscopic investigation.

Explicitly correlated coupled cluster theory at the CCSD(T*)-F12b level (T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys., 2007, 127, 221106) and two precise spectroscopic parameters (K. Kawaguchi, J. Chem. Phys., 1988, 88, 4186) were used to construct an accurate near-equilibrium analytical potential energy function (PEF) for the highly anharmonic centrosymmetric hydrogen-bonded complex ClHCl(-) (Re = 3.1153 Å). From variational calculations with that PEF, a large number of rovibrational energies of different isotopologues up to high values of the rotational quantum number J was obtained. Theory helped with the assignment of lines observed by IR diode laser spectroscopy in the ν1 + ν3 combination band of (35)ClH(35)Cl(-) and (37)ClH(35)Cl(-) and enabled us to elucidate rather subtle patterns of rovibrational interactions. Furthermore, transition dipole moments were predicted and analysed as well as unusual isotopic effects.

Coherence decay measurement of v = 2 vibrons in solid parahydrogen.

The coherence decay of the v = 2 vibrational state (vibrons) of solid parahydrogen was measured via time-resolved coherent anti-Stokes Raman spectroscopy. We found that the decay curve has a non-exponential time profile in the time scale of 200 ns at a low temperature below 5 K and a low orthohydrogen impurity concentration (~0.01%). This behavior, as also observed in the case of the v = 1 vibrons, represents a signature of band structure of the v = 2 state in the solid phase. The maximum coherence decay time of 50 ns in an exponential part was achieved, which shows excellence of the v = 2 state for coherent processes. We also found that finite temperatures, orthohydrogen impurities, and other structural inhomogeneity accelerate the decay, hiding the non-exponential feature of the vibron band.

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.

High-resolution Fourier transform infrared absorption spectroscopy of the ν6 band of c-C3H2.

The gas-phase high-resolution absorption spectrum of the ν(6) band of cyclopropenylidene (c-C(3)H(2)) has been observed using a Fourier transform infrared spectrometer for the first time. The molecule has been produced by microwave discharge in an allene (3.3 Pa) and Ar (4.0 Pa) mixture inside a side arm glass tube. The observed spectrum shows a pattern of c-type ro-vibrational transitions in which the Q-branch lines strongly and distinctly stand out in the spectrum. A combined least-squares analysis of the observed 216 ro-vibrational transitions together with 28 millimeter-wave rotational transitions from the previous study has resulted in an accurate determination of the molecular constants in the ν(6) state. The band center is found to be at 776.11622(13) cm(-1) with one standard deviation in parentheses, which is 2.3% lower than the matrix isolation value. The intensity ratio I(3)(ν(3))/I(6)(ν(6)) obtained from the observed ν(3) and ν(6) bands, 1.90(9), is somewhat lower than the ratio estimated from ab initio (2.4-2.6) and DFT (2.8) calculations.

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).

Analyses of the infrared absorption bands of (15)NO(3) in the 1850-3150 cm(-1) region.

We have observed the infrared spectrum of (15)NO(3) by a high resolution Fourier transform infrared (FT-IR) spectrometer using the reaction of F atoms with H(15)NO(3). Five (2)E'-(2)A(2)' bands are identified in the 1850-3150 cm(-1) region. The rotational analyses indicate that these bands have the lower state in common, which coincides with the ground state of planar D(3h) symmetry. The upper (2)E' states more or less suffer from perturbations by close-lying dark states. Among them, those of the 2004, 2128, and 2492 cm(-1) bands are analyzed to determine molecular parameters in these states by fixing the ground-state constants to those derived by a combination difference method. The spin-orbit and Coriolis coupling constants in the (2)E' states are substantially different for different vibronic states. The vibrational assignments of NO(3) in the ground electronic state are discussed using experimental data heretofore available, supplemented by those obtained by the present study.