Formation and detection of metastable formic acid in a supersonic expansion: High resolution infrared spectroscopy of the jet-cooled cis-HCOOH conformer.

High-resolution direct absorption infrared spectra of metastable cis-formic acid (HCOOH) trapped in a cis-well resonance behind a 15 kcal/mol barrier are reported for the first time, with the energetically unstable conformer produced in a supersonic slit plasma expansion of trans-formic acid/H mixtures. We present a detailed high-resolution rovibrational analysis for cis-formic acid species in the OH stretch (ν) fundamental, providing first precision vibrational band origin, rotational constants, and term values, which in conjunction with ab initio calculations at the couple-cluster with single, double, and perturbative triple [CCSD(T)]/ANOn (n = 0, 1, 2) level support the experimental assignments and establish critical points on the potential energy surface for internal rotor trans-to-cis isomerization. Relative intensities for a- and b-type transitions observed in the spectra permit the transition dipole moment components to be determined in the body fixed frame and prove to be in good agreement with ab initio CCSD(T) theoretical estimates but in poor agreement with simple bond-dipole predictions.

High-resolution infrared spectroscopy of jet cooled CHBr radicals: The symmetric CH stretch manifold and absence of nuclear spin cooling.

Direct laser absorption of a slit supersonic discharge expansion provides the first high-resolution spectroscopic results on the symmetric CH stretch excitation (ν) of the bromomethyl (CHBr) radical in the ground electronic state. Narrowband (<1 MHz) mid-infrared radiation is produced by difference-frequency generation of two visible laser beams, with the open shell halohydrocarbon radical generated by electron dissociative attachment of CHBr in a discharge and rapidly cooled to T = 18 ± 1 K in the subsequent slit-jet supersonic expansion. A rovibrational structure in the radical spectrum is fully resolved, as well as additional splittings due to spin-rotation effects and Br/Br isotopologues in natural abundance.

High-resolution infrared spectroscopy of HCF in the CH stretch region.

We present the results from a high-resolution infrared study of jet-cooled singlet monofluorocarbene (HCF) in the CH stretch region near 2600 cm. Absorption signals are recorded using near quantum shot noise limited laser absorption methods. The fully resolved absorption spectra of the CH stretch (ν) fundamental band and a partial progression of transitions of the HCF bend plus CF stretch (ν + ν) combination band are observed and show clear evidence of a strong rovibrational coupling between the νK = 2 and ν + νK = 3 manifolds, including the observation of "dark state" transitions.

Stretching our understanding of C: Experimental and theoretical spectroscopy of highly excited nν + mν states (n ≤ 7 and m ≤ 3).

We present the high resolution infrared detection of fifteen highly vibrationally excited nν + mν combination bands (n ≤ 7 and m ≤ 3) of C produced in a supersonically expanding propyne plasma, of which fourteen are reported for the first time. The fully resolved spectrum, around 3 μm, is recorded using continuous wave cavity ring-down spectroscopy. A detailed analysis of the resulting spectra is provided by ro-vibrational calculations based on an accurate local ab initio potential energy surface for C (X̃Σ).

High-Resolution Infrared Spectra of the ν Fundamental Bands of Mono-Substituted C Propyne Isotopologues.

We present a combined experimental and ab initio study on the jet-cooled high-resolution infrared spectra of the ν (acetylenic stretch) fundamental band for three isotopologues of propyne: CHC≡CH, CHC≡CH, and CHC≡CH. The experimental spectra are recorded in natural abundance using a continuous supersonic expansion of regular propyne diluted in argon and helium, in combination with continuous wave cavity ring-down spectroscopy (cw-CRDS). The fully rotationally resolved K' = 0 and 1 subbands of all three monosubstituted C isotopologues have been measured near 3330 cm, and their spectroscopic analysis is presented here for the first time.

Theoretical investigation of the infrared spectrum of small polyynes.

The full cubic and semidiagonal quartic force fields of acetylene (CH), diacetylene (CH), triacetylene (CH), and tetraacetylene (CH) are determined using CCSD(T) (coupled cluster theory with single and double excitations and augmented by a perturbative treatment of triple excitations) in combination with the atomic natural orbital (ANO) basis sets. Application of second-order vibrational perturbation theory (VPT2) results in vibrational frequencies that agree well with the known fundamental and combination band experimental frequencies of acetylene, diacetylene, and triacetylene (average discrepancies are less than 10 cm). Furthermore, the predicted ground state rotational constants (B) and vibration-rotation interaction constants (α) are shown to be consistent with known experimental values.