Millimeter-Wave and High-Resolution Infrared Spectroscopy of the Ground and Seven Lowest Fundamental States of 1H-1,2,4-Triazole.

A combined analysis of millimeter-wave (70-700 GHz) and rotationally resolved infrared (400-1200 cm-1) spectra of the ground state and seven fundamental vibrational modes of 1H-1,2,4-triazole is reported. While the lowest-energy vibrationally excited state (ν18) is well-treated using a single-state distorted-rotor Hamiltonian, the second (ν17) and third (ν16) vibrationally excited states are involved in strong c-type Coriolis coupling and require an appropriate two-state Hamiltonian. The oblate nature of 1H-1,2,4-triazole is sufficiently close to the oblate symmetric-top limit that the analysis requires the use of A-reduced, sextic centrifugally distorted-rotor Hamiltonian models in the Ir representation in order to achieve low σfit values. The coupling between ν17 (A″) and ν16 (A″) resulted in many transitions with slightly perturbed frequencies, many highly displaced resonant intrastate transitions, and 165 nominal interstate transitions. Modeling the spectra of ν17 and ν16 required three c-axis Coriolis-coupling terms (Fab, FabJ, and FabK) to treat the interaction. Many of the nominal interstate transitions form clearly discernible Q-branch bands, comprising degenerate sets of a- and b-type transitions. The rotational spectra of four higher-energy vibrationally excited states (ν15, ν14, ν13, and ν12), which form a complex polyad involving Coriolis and anharmonic coupling interactions, were analyzed by single-state models, thus producing only effective spectroscopic constants. Inclusion of rotationally resolved infrared transitions enabled the accurate and precise determination of vibrational band origins for the four lowest-energy fundamental states: ν18 = 542.601 824 3 (28) cm-1, ν17 = 665.183 128 5 (43) cm-1, ν16 = 682.256 910 5 (43) cm-1, and ν15 = 847.557 400 (11) cm-1.

Millimeter/Submillimeter-wave Spectroscopy and the Semi-experimental Equilibrium (reSE) Structure of 1H-1,2,4-Triazole (c-C2H3N3).

The millimeter/submillimeter spectrum of 1H-1,2,4-triazole is reported from 70 to 700 GHz, providing spectral frequencies directly comparable to radio telescopes and enabling an astronomical search. Using four deuteriated samples of 1,2,4-triazole, we measured, assigned, and least-squares fit transitions for 26 isotopologues to sextic A- and S-reduced Hamiltonians. An accurate and precise semi-experimental (reSE) structure from 50 independent moments of inertia has been obtained. Structural parameters are provided with 2σ uncertainties within 0.0009 Å for bond distances and 0.09° for bond angles. The structural parameters are in quite good agreement with the best theoretical estimate (BTE) obtained using CCSD(T)/cc-pCV5Z, where an agreement within the 2σ uncertainty is observed for all but one case. Despite the large number of isotopologues already included in this structure, more may be useful. One isotopologue, [1,3-2H]-1H-1,2,4-triazole, is observed to closely approach the oblate asymmetric-top limit, resulting in a clear breakdown of the A-reduction Hamiltonian. The highly accurate reSE structure and subsequent analysis demonstrates that the S-reduction is also unable to adequately model the spectrum of this isotopologue.

Laser-Induced Chemistry Observed during 248 nm Vacuum Ultraviolet Photolysis of an O3 and CH3NH2 Mixture.

We present an examination of the 248 nm VUV (vacuum ultraviolet) laser photolysis of an ozone (O3) and methylamine (CH3NH2) mixture as means to produce aminomethanol (NH2CH2OH). Aminomethanol is predicted to be the direct interstellar precursor to glycine and is therefore an important target for detection in the interstellar medium. However, due to its high reactivity under terrestrial conditions, aminomethanol evades gas-phase spectral detection. The insertion of O(1D) into methylamine is one proposed pathway to form aminomethanol. However, this formation pathway is highly exothermic and results in a complex mixture of reaction products, complicating spectral assignment. Additional reactions between methylamine and the other products of ozone photolysis lead to further complication of the chemistry. Here, we present a systematic experimental study of these reaction pathways. We have used direct absorption millimeter/submillimeter spectroscopy in a supersonic expansion to probe the reaction products, which include formaldehyde (H2CO), methanimine (CH2NH), formamide (HCONH2), and hydrogen cyanide (HCN) and absorption signals arising from at least two additional unknown products. In addition, we examine the effects of reaction time on the chemical formation pathways and discuss them in the context of O(1D) insertion chemistry with methylamine. We have built a kinetics box model to interpret the results that are observed. We then examine the implications of these results for future studies aimed at forming and detecting aminomethanol.