Theoretical spectra and energetics for c-C3HC2H, l-C5H2, and bipyramidal D3h C5H2

Abstract

The recent astronomical detection of c-C3HC2H and l-C5H2 has led to increased interest in C5H2 isomers and their relative stability. The present work provides the first complete list of anharmonic vibrational spectral data with infrared intensities for three such isomers as well as including the first set of rotational data for the bipyramidal C5H2 isomer allowing for these molecules to serve as potential tracers of interstellar carbon. All three isomers have fundamental vibrational frequencies with at least one notably intense fundamental frequency. The l-C5H2 isomer has, by far, the highest intensities out of the three isomers at 2076.3 cm−1 (738 km mol−1) and 1887.5 cm−1 (182 km mol −1). The c-C3HC2H isomer has one intense peak at 3460.6 cm−1 (84 km mol−1), and the bipyramidal C5H2 isomer has one intense peak at 489.3 cm−1 (78 km mol−1). The relative intensities highlight that while l-C5H2 is not the lowest energy isomer, its notable intensities should make it more detectable in the infrared than the lower energy c-C3HC2H form. The bipyramidal isomer is firmly established here to lie 44.98 kcal mol−1 above the cyclic form. The explicitly correlated coupled cluster rovibrational spectral data presented herein should assist with future laboratory studies of these C5H2 isomers and aid in detection in astronomical environments especially through the newly operational James Webb Space Telescope.

The fundamental vibrational frequencies and spectroscopic constants of the C2O2H2 isomers: molecules known in simulated interstellar ice analogues

“…As such, the present work will fill in the knowledge gap for these molecules and will provide accurate spectroscopic classification for the five lowest-energy, C 2 O 2 H 2 isomers in a manner similar to that for ethynol, 22,28 methanediol, 16,29,30 and diaminomethane. 31,32 The existence of the trans-glyoxal gas phase, experimental fundamental vibrational frequencies will allow for benchmarking of the employed quantum chemical methods, and such findings will give clear error expectations for the fundamental frequencies and spectroscopic constants for the other computed isomers. The present approach in this work will employ the venerable quartic force field (QFF) for approximating the anharmonic potential about the minimum and will be conjoined to second-order rotational and vibrational perturbation theory (VPT2).…”

Linear BeNCO and OBeNC: kinetically stable neutral Be-bearing free molecules

“…However, the configuration shows a clear linear trend when the O and N atoms bind with alkaline earth metals; this linear trend increases with a decrease in the electronegativity of the alkaline earth metal and an increase in the ionic bonding component. For instance, in BeOH, [24][25][26] XBeOH (X = CH 3 , 26,27 H 28,29 ), and HBeX (X = OCN, OCH 3 ), 30 the Be-O-Y (Y = H or C) bond angles are approximately 1401, whereas in MOH (M = Mg-Ba), 24,25,31,32 HMgX (X = OH, OCH 3 , NCO, OCN), 28,[33][34][35][36] and HOMgY (Y = CH 3 , CN, NC), [36][37][38][39] the molecular backbone chains are linear or quasi-linear at equilibrium. Previous studies on the potential interstellar molecular system [Mg,N,C,O] show that MgNCO and MgOCN are linear, whereas MgONC has a Mg-O-C bond angle of 1251.…”

Stereo-electronic factors influencing the stability of hydroperoxyalkyl radicals: transferability of chemical trends across hydrocarbons and ab initio methods

“…12 Further, when it is challenging to associate experimental spectra of transient species with multiple potential isomers, computational findings provide valuable insights. 18,19 For modelling low-temperature combustion reactions of small hydrocarbons, coupled cluster singles doubles with perturbative triples approximation, CCSD(T), has yielded highly accurate predictions. 20,21 For larger molecules, composite wavefunction theories have demonstrated the best computational efficiency for reproducing experimental formation enthalpies of stable species [22][23][24][25][26][27] and for accurate modelling of barrier heights.…”