High-resolution cavity ring-down spectroscopic investigation of the fundamental symmetric stretch (ν1) band of 14N15N16O isotopologue in the 7.8 μm mid-IR region

Ground-state infrared spectra of the syn and anti conformers of jet-cooled 5-hydroxytropolone (5-HOTrOH) monomer have been recorded free from interference from one another using a fluorescence depletion method. The 5-hydroxy group "free" O−H stretch, 2-hydroxy intramolecularly hydrogen-bonded O−H stretch, and C−H stretch transitions are observed for both conformers. The assignment of these bands is clear by comparison with previous infrared studies of bare tropolone and is confirmed by MP2 and DFT level vibrational frequency and intensity calculations. Each of the conformers is predicted to have four allowed C−H stretch transitions. There is a reasonable one-for-one correspondence between calculation and experiment for the anti conformer's C−H stretch bands, while the syn conformer shows effects of Fermi resonance mixing. The 5-OH stretch bands of the syn and anti conformers are single, sharp transitions located at 3654 and 3664 cm-1, respectively. The OH stretch fundamentals of the 2-OH group involved in the intramolecular hydrogen bond are centered on 3170 and 3195 cm-1. These bands are extensively broadened in both conformers and contain reproducible substructure with irregular spacing of about 10−15 cm-1. The substructure of the intramolecularly H-bonded 2-hydroxy O−H stretch band reflects a selective first-tier vibrational-state mixing, most likely with a set of modes which are in near two-to-one resonance with it. Finally, the 249 cm-1 asymmetry in the double-minimum potential well for H atom tunneling appears to be sufficient to quench syn−anti tunneling in S0 even following excitation of the 2-OH stretch fundamental. No evidence is found for syn ↔ anti "crossover" transitions despite careful searches capable of detecting such transitions at depletion levels of about 1%.

Time-resolved infrared diode laser spectroscopy of the ν1 (C–O stretch) band of the CoCO radical

Lithium perchlorate solutions in acrylonitrile (propenenitrile), in a range of concentration between 1 and 6 molal, were studied by using Fourier transform Raman spectroscopy. The new band in the v(CN) region proceeding from the bound species Li+… (acrylonitrile)n and the modifications in the C—C stretching band were studied in detail by means of deconvolution and band‐fitting procedures. An average solvation number of ca. 2.3 was obtained without any correction for the ion pairing. The data obtained in the analysis of the perchlorate anion v1 (symmetric stretch) band allow us to quantify the concentration of the different species (free perchlorate, solvent‐separated ion pairs and contact ion pairs) present, and to obtain a more realistic solvation number for the lithium ion in acrylonitrile solutions. This solvation number was estimated at 3.0 ± 0.1.

ABSTRACTWe present the first investigation of the ν8 band (C–C symmetric stretch at 870.3137 cm−1), together with an extended analysis of the neighbouring ν21 band (CH3 rock at 921.3756 cm−1) of propane (C3H8). Our previous investigation of the ν21 A-type band [A.Perrin, F. Kwabia-Tchana, J.M.Flaud, L.Manceron, P.Groner, W.J.Lafferty. J. Mol. Spectrosc. 315, 55 (2015)] revealed that the rotational energy levels of 211 are split because of interactions with the internal rotations of the methyl groups, leading to the identification of AA, EE, AE and EA torsional components. In this work, a similar behaviour was observed for the B-type ν8 band and the analysis of the ν21 band was greatly extended. One of the results of the present study is to show that these torsional splittings are due to the existence of anharmonic and Coriolis resonances, coupling the 211 and 81 rotational levels to nearby highly excited levels of the two internal rotations of the methyl groups. Accordingly, an effective ‘vibration – torsion- rotation’ Hamiltonian model was built in the G36 symmetry group which accounts for both types of resonances. In parallel, a code computing the line intensities was developed to allow unambiguous torsional component assignments. The line assignments were performed using a high resolution (0.0015 cm−1) infrared spectrum of propane, recorded with synchrotron radiation at the SOLEIL French light source facility coupled to a Bruker IFS-125 Fourier transform spectrometer. Finally, a linelist of positions and intensities which can be used for the detection of propane in the Earth and outer planets atmospheres was produced.

Velocity-map ion imaging has been used to study the vibrational predissociation dynamics of the HCl dimer following infrared (IR) excitation in the HCl stretch overtone region near 1.77 Å. HCl monomer predissociation products were detected state-selectively using 2 + 1 resonance-enhanced multiphoton ionization spectroscopy. The IR action spectrum shows the free HCl stretch (2ν1), the bound HCl stretch (2ν2), and a combination band involving the intermolecular van der Waals stretching mode (2ν2 + ν4). Fragment speed distributions extracted from ion images obtained for a range of HCl(v = 0, 1; J) levels following vibrational excitation on the 2ν1 and 2ν2 bands yield the correlated product pair distributions. All product pairs comprise HCl(v = 1) + HCl(v = 0) and show a strong propensity to minimize the recoil kinetic energy. Highly non-statistical and mode-dependent HCl product rotational distributions are observed, in contrast to that observed following stretch fundamental excitation. Predissociation lifetimes are also mode-dependent: excitation of the free HCl leads to τVP = 13 ± 1 ns, while the bound stretch has a shorter lifetime τVP ≤ 6 ns. The dimer dissociation energy determined from energy conservation (D0 = 397 ± 7 cm-1) is slightly smaller than the previously reported values. The results are discussed in the context of previous observations for (HF)2 and (HCl)2 after excitation of HX stretch fundamentals and models for vibrational predissociation.

Solutions of magnesium or calcium perchlorate in acrylonitrile (propenenitrile), in a range of concentrations [1–3 mol kg–1 for Mg(ClO4)2 and 1–6 mol kg–1 for Ca(ClO4)2], have been analysed by FT-Raman spectroscopy. The new bands in the ν(CN) region arising from the bound species, M2+⋯(acrylonitrile)n, have been examined in detail using deconvolution and band-fitting procedures. Solvation numbers of six (at infinite dilution) were calculated for both cations. The data obtained in the analysis of the perchlorate anion ν1(symmetric stretch) band show important differences in the association behaviour of the cations. Solutions of magnesium perchlorate indicate the presence of only one associated species. On the other hand, calcium perchlorate solutions show more complicated features and up to three different associated species could be identified. The stoichiometry and structures of these coordination species are discussed.

The O-D stretch fundamental region of the deuterated water dimer, (D2O)2, is further studied using a pulsed supersonic slit jet and a tunable optical parametric oscillator infrared source. The previously unobserved acceptor symmetric O-D stretch fundamental vibration is detected, with Ka = 0 ← 0 and 1 ← 0 sub-bands at about 2669 and 2674cm-1, respectively. The analysis indicates that the various water dimer tunneling splittings generally decrease in the excited vibrational state, similar to the three other previously observed O-D stretch fundamentals. Two new (D2O)2 combination bands are observed, giving information on intermolecular vibrations in the excited O-D stretch states. The likely vibrational assignments for these and a previously observed combination band are discussed.

High-resolution investigation of temperature and pressure-induced spectroscopic parameters of 13C-isotopomer of CH4 in the ν4 band using cavity ring-down spectroscopy

The silicate component of Martian dust

The rotationally resolved spectra of Ne–C2H2 and Ne–C2HD were measured in the region of the asymmetric C–H stretch (ν3) band of the acetylene monomer. The transitions in the Ne–C2H2 spectrum are substantially broadened by vibrational predissociation, while those of Ne–C2HD are quite narrow. This difference is attributed to the fact that in the former dissociation proceeds through a “doorway” state, related to a Fermi resonance involving the bending vibrations of C2H2. In C2HD this Fermi resonance is absent. The potential energy surface (PES) for the Ne–acetylene complex has been computed using symmetry-adapted perturbation theory. This PES has been fit to an analytic form and applied in calculations of the rovibrational energy levels of Ne–C2H2 and Ne–C2HD. From these levels and calculated transition intensities we generated the near-infrared spectra of these complexes in the region of the ν3 band. These complexes may be considered as nearly free internal rotors. For Ne–C2H2 the results obtained from the ground state PES gave semiquantitative agreement with the measured spectrum. For Ne–C2HD we could assign all of the (much sharper) lines in the experimental spectrum and obtain the ν3 excited state interaction potential from a fit of the calculated spectrum to the experimental one. The ground state ab initio potential was not altered in this fit; the excellent agreement between the calculated and measured infrared spectrum for Ne–C2HD demonstrates that our Ne–acetylene potential is quite accurate.

294 transitions were measured by velocity modulation spectroscopy using a difference frequency laser system with a D2/O2 discharge and assigned to the ν3 (antisymmetric stretch) band of D3O+. A simultaneous analysis of this data with the ν2 band spectra reported by Sears, et al. [J. Chem. Phys. 83, 2676 (1985)] yielded a refined set of parameters for both the ground and the excited states of both bands. The ν3 bandcenters are 2629.6512(39) and 2624.2376(47) cm−1 for the s–s and a–a inversion components, respectively.

On the ν12 band of C6D6 at 2289 cm−1

We use optical frequency comb Fourier transform spectroscopy to measure high-resolution spectra of iodomethane, CH3I, in the CH stretch region from 2800 to 3160 cm-1. The fast-scanning Fourier transform spectrometer with auto-balanced detection is based on a difference frequency generation comb with repetition rate, frep, of 125 MHz. A series of spectra with sample point spacing equal to frep are measured at different frep settings and interleaved to yield sampling point spacing of 11 MHz. Iodomethane is introduced into a 76 m long multipass absorption cell by its vapor pressure at room temperature. The measured spectrum contains three main ro-vibrational features: the parallel vibrational overtone and combination bands centered around 2850 cm-1, the symmetric stretch ν1 band centered at 2971 cm-1, and the asymmetric stretch ν4 band centered at 3060 cm-1. The spectra of the ν4 band and the nearby ν3+ν4-ν3 hot band are simulated using PGOPHER and a new assignment of these bands is presented. The resolved ro-vibrational structures are used in a least square fit together with the microwave data to provide the upper state parameters. We assign 2603 transitions to the ν4 band with a standard deviation (observed – calculated) of 0.00034 cm-1, and 831 transitions to the ν3+ν4-ν3 hot band with a standard deviation of 0.00084 cm-1. For comparison, in the earlier work using standard FT-IR with 162 MHz resolution [Anttila, et al., J. Mol. Spectrosc. 1986; 119:190–200] 1830 transition were assigned to the ν4 band, and 380 transitions to the ν3+ν4-ν3 hot band, with standard deviations of 0.00083 cm-1 and 0.0013 cm-1, respectively. The hyperfine splittings due to the 127I nuclear quadrupole moment are observed for transitions with J ≤ 2 × K. Finally, intensities of 157 isolated transitions in the ν4 band are reported for the first time using the Voigt line shape as a model in multispectral fitting.

The Raman spectrum of the 13CH12CH molecule in the region of its ν2 vibrational band was recorded at a resolution of 2.6 × 10−3 cm−1 and analyzed. Several Q branches were observed and identified, corresponding to the ν2 fundamental and the associated hot bands ν2 + ν4 – ν4, ν2 + ν5 – ν5, ν2 + 2ν4 – 2ν4 and 2ν2 – ν2. The usual normal modes of vibration in acetylene, with the symmetric (ν1) and antisymmetric (ν3) CH stretchings, the CC stretching (ν2), the degenerate trans (ν4) and cis (ν5) bendings were adopted. All the spectra were obtained using the experimental technique of quasi‐continuous stimulated Raman spectroscopy. The fundamental ν2 band and the ν2 + ν4 – ν4 and ν2 + ν5 – ν5 hot bands were recorded at room temperature, while ν2 + 2ν4 – 2ν4 was recorded at a temperature of 355 K. Finally, the spectrum of the 2ν2 – ν2 band was recorded at 170 K using a Raman‐Raman double resonance technique in which a stimulated Raman pumping process is used to populate a single rotational level of the v2 = 1 state, prior to the spectroscopy stage. A 15 ns delay between pump and spectroscopy is introduced to allow partial collisional relaxation of the rotational population of v2 = 1 among rotational levels. The assigned Raman transitions and several previously observed infrared bands have been simultaneously fitted in order to derive a set of deperturbed molecular parameters, including the quartic anharmonic coupling coefficients K1,255 and K3,245. The ro‐vibrational pattern of the stretching and stretching‐bending combination states and an accurate description of the anharmonic resonances in this molecule have been obtained. Copyright © 2013 John Wiley & Sons, Ltd.

The ν2 (N–O stretch) fundamental bands of HNO and DNO and the ν3 (bending) band of HNO in the 6.5 μm region have been studied using the technique of laser Stark spectroscopy. The experiment utilized a Stark cell located inside the cavity of a CO laser, with the short-lived HNO molecules produced in a flow system by the reaction H+NO→HNO. Accurate values for the band origins, rotational constants, and dipole moments were obtained from analyses of 35 transitions in DNO and over 40 in HNO. The Coriolis interaction between the close-lying ν2 and ν3 states of HNO was explicitly included in the analysis, enabling a value for the Coriolis interaction parameter to be derived. A few transitions in the ν1 (N–D stretch) band of DNO near 5 μm were also detected from which a tentative value of the band origin was estimated.