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The spectra of C1 molecules are confounding in that each of the fundamental vibrational modes transform as the same irreducible representation (A) and hence each band consists of a seemingly random distribution of a-, b-, and c-type transitions. This is in contrast to higher symmetry molecules for which band types are readily deduced by simple symmetry rules. Herein, we present a method to simulate the convoluted rotational contours in the gas-phase spectra of C1 molecules by combining existing ab initio calculations with Colin Western’s pgopher rotational contour program. Specifically, ab initio calculations in the NWChem suite of programs were employed to predict the components of the dipole moment derivatives along the principal axes of the moments of inertia. This information was then input into pgopher to model the fundamental band contours as a sum of a-, b-, and c-type transitions. This method was applied to simulate the rotational contour spectra of a series of representative C1 molecules which were then compared against both ab initio stick spectra and experimentally measured broadband IR spectra from the Pacific Northwest National Laboratory infrared gas-phase database. In addition to providing further insight beyond what is revealed in a typical stick spectrum, the simulated contours showed good agreement with the measured spectra.

Vibrationally mediated photodissociation dynamics of jet-cooled H2O in the vOH=2 polyad is studied in a supersonic slit jet expansion. Single rotational states within |02〉− (≡ν1+ν3 in normal mode notation), |02〉+(≡2ν1), |11〉+(≡2ν3), and |01−2〉(≡ν3+2ν2) vibrational states of H2O are selectively prepared with near IR overtone pumping, photodissociated at 193 nm, and the resulting nascent internal state distribution of OH fragments probed via laser induced fluorescence. Strong oscillations in rotational, spin–orbit, and lambda-doublet distributions are observed, often in remarkably close agreement with H2O state-to-state photodissociation studies from both higher and lower vOH polyads. The influence of initially excited bending and JKaKc levels of H2O on spin–orbit, Λ-doublet, and rotational distributions of OH is examined in detail. Several new dynamical trends are identified, for example, a clear propensity at high N for a strong Λ+ versus Λ− inversion in the Π3/2 spin–orbit manifold, which reverses in the...

High-resolution vibrationally mediated IR+UV photodissociation methods are used to investigate the dynamics of H–OH bond breaking in quantum state selected H2O and Ar–H2O van der Waal complexes prepared in a slit supersonic jet expansion. This capability is based on the following strategy: (i) Specific rovibrational quantum states of the Ar–H2O dimer and H2O monomer are optically selected in the second overtone (vOH=3←0) region with an injection seeded, Fourier transform limited (Δν≈160 MHz) optical parametric oscillator. (ii) Selective H–OH bond cleavage of the vibrationally excited H2O subunit in the cluster is achieved by 248 nm or 222 nm UV photolysis. (iii) Multibody collision dynamics between the H, OH, and Ar photofragments are probed via laser induced fluorescence (LIF) on the asymptotic OH rotational, lambda-doublet and spin–orbit distributions. Comparison between cluster (Ar–H2O) and monomer (H2O) data explicitly samples the influence of the Ar “solvent” on the UV photolysis dynamics and in part...

The dissociation of nitric acid upon πnb,O→πNO2* excitation at 193 nm has been studied in a crossed laser-molecular beam apparatus. The primary reaction channels are OH+NO2 and O+HONO. We measure the branching ratio between these two competing processes and determine (OH+NO2)/(O+HONO)=0.50±0.05. Our experiments provide evidence of a minor O+HONO pathway, which we assign to O(3P) and HONO in its lowest triplet state. The dominant pathway correlates to O(1D)+HONO(X 1A′). The translational energy distributions reveal two distinct pathways for the OH+NO2 channel. One pathway produces stable NO2 fragments in the 1 2B2 electronic state. The second pathway produces unstable NO2 fragments which undergo secondary dissociation to NO+O. We examine the influence of nonadiabaticity along the OH+NO2 reaction coordinate in order to explain the significant branching to this other channel. Finally, we introduce a new method for generating correlation diagrams for systems with electronic transitions localized on one moiety...

The experiments presented here investigate the competing photodissociation pathways for allyl chloride upon excitation of the nominally ππ*(C=C) transition at 193 nm. The measured photofragment velocity distributions evidence C–Cl bond fission and HCl elimination. The recoil kinetic energy distribution for the HCl products is bimodal, indicating two primary processes for HCl elimination. The experimental measurements show C–Cl bond fission dominates, giving an absolute branching ratio of HCl:C–Cl=0.12±0.03 when the parent molecule is expanded through a nozzle at 200 °C. The branching ratio depends on the nozzle temperature; at 475 °C, the absolute branching ratio measured is HCl:C–Cl=0.24±0.03. We analyze the experimental results along with supporting ab initio calculations and earlier photodissociation studies of vinyl chloride in order to examine the potential influence of nonadiabaticity along the C–Cl fission reaction coordinate and its dependence on molecular conformation.