Predissociation Mechanism and Dynamics of HCP

Esposito

Francisco

2023

ApJ

We obtained accurate vibrational frequencies, rotational constants, and vertical transition energy for AlNH2(X1A1) and HAlNH(X1A′) isomers using ab initio calculations at various levels of theory. These two isomers are potential candidates for astronomical observation. AlNH2 and HAlNH are thermodynamically stable, with Al-NH2 and HAl-NH bond dissociation energies predicted to be 4.39 and 3.60 eV, respectively. The two isomers are characterized by sizable dipole moments of 1.211 and 3.64 D, respectively. The anharmonic frequencies and spectroscopic constants reported for the two isomers should facilitate their experimental differentiation. In addition, we evaluated the evolution of the low-lying electronic states along the stretching coordinates, as well as the absorption cross sections. AlNH2 absorbs strongly around 287, 249, and 200 nm, whereas the HAlNH absorption is centered around 370 and 233 nm.

Section: Introductionmentioning

confidence: 99%

Vibrational, Rotational, and Electronic Spectroscopy for Possible Interstellar Detection of AlNH₂ and HAlNH

Esposito

Francisco

2023

ApJ

“…For instance, in the gas phase, PO is formed via the reaction P + OH → PO + H, while the formation of PN depends on the abundance of PO through N + PO → PN + O (Jiménez-Serra et al 2018;García de la Concepción et al 2021). The CP radical is the daughter of HCP (Namai et al 2009;Agúndez et al 2007), that is HCP + hν → CP + H following the photodesorption of HCP from the surface of dust grains. Other P-bearing molecules may exist, especially those containing PO, PN, or PS bonds.…”

Section: Introductionmentioning

confidence: 99%

Astrochemical significance and spectroscopy of tetratomic [H, P, S, O]

Esposito

Friskey

et al. 2022

A&A

Context. Phosphorus is integral to life on Earth, and its role in the chemistry of the interstellar medium is highly debated and unknown. Only a handful of phosphorus-bearing species have been detected thus far, with the most recent confirmed detection taking place in 2014. The simultaneous detection of molecules such as PO, SH, and OH indicate the possibility of reactive intermediate species existing in the interstellar medium and circumstellar envelopes of evolved stars. To explore this possibility, the [H, P, S, O] tetratomic isomer family was characterized using high level ab intio methods. Aims. The aim of this study is to provide rotational, vibrational, and electronic spectroscopic data to drive experimental and observational detection of new phosphorus and sulfur-bearing molecules. Additionally, chemical pathways are explored to explain possible reservoirs for the as of yet undetected PH and PS diatomic molecules. Methods. Coupled cluster quantum chemistry methods were used to calculate the equilibrium electronic structure followed by the anharmonic treatment of the cubic and quartic force fields to obtain accurate rotational and vibrational data. Møller-Plesset perturbation theory in conjunction with coupled cluster methods were used to explore bimolecular reaction pathways. Multi-reference methods were then used to characterize the photochemical pathways of the excited electronic states and simulate the electronic absorption spectrum.Results. The reaction between detected molecules SH and PO is highly exothermic and forms the HSPO isomer. Deeply submerged transition state barriers allow for facile isomerization to other isomers, especially HOPS. The dominant photochemical process predicted for HOPS is dissociation to form OH + PS, while that of HSPO is a combination of photodissociation to form H + SPO and SH + PO, depending on the wavelength of light absorbed. If PH and PS are formed in the early outflows from evolved stars, bimolecular reactions may act as a reservoir and partially account for their lack of detection to date. The electronic absorption spectrum is predicted to be congested in the 175 -200 nm region for both HOPS and HSPO. Differentiating peaks exist > 400 nm, which can be used for spectral assignment. Vibrationally corrected rotational constants and anharmonic vibrational frequencies were calculated to assist in the laboratory and observation identification of the most stable molecules. The PO stretch is predicted to be the most intense vibrational mode in both HOPS isomers, and a frequency difference of 20 cm −1 may prove to help differentiate the conformers in an experimental spectrum.

“…Depending on the temperature and radius of the envelope, many plausible mechanisms have been proposed to explain the formation of phosphorus-bearing molecules. On the one hand, diatomic species such as CP, PO, PN and PH may be products of triatomic parent species such as HCP, i.e., HCP + hH + CP (Namai et al 2009), or another phosphorus-bearing parent molecule, such as PNO or HPO. In this case, the photodissociation mechanism may explain the formation of the diatomic species, and the known electronic spectroscopy proprieties of the parent molecules provide important insight into this mechanism.…”

Section: Introductionmentioning

confidence: 99%

Astrochemical Significance of the P + SO Reaction: Spectroscopic Characterization of SPO, PSO, and SOP Isomers

Plane

Francisco

2021

ApJ

The doublet and quartet potential energy surfaces for the P + SO → PO + S reaction are explored using the highly accurate explicit correlation multireference configuration interaction method, and the reaction is found to be thermodynamically favorable, with an exothermicity value of 70.5 kJ mol−1. The electronic structure, spectra, and bond dissociation energies of the intermediates involved in the reaction, such as SPO, PSO, and SOP, are calculated using high-level quantum chemistry methods. An explanation of the nondetection of the diatomic SP is proposed. At pressures relevant to astrochemistry, the reaction is overwhelmingly bimolecular, with a predicted rate coefficient of 2.1 × 10−10 (T/300)−0.23 cm3 molecule−1 s−1. The results from this study are expected to aid in the spectroscopic detection of these new species in the laboratory and the interstellar medium.