High-Level Rovibrational Calculations on Ketenimine

Abstract

From an astrochemical point of view ketenimine (CH2CNH) is a complex organic molecule (COM) and therefore likely to be a building block for biologically relevant molecules. Since it has been detected in the star-forming region Sagittarius B2(N), it is of high relevance in this field. Although experimental data are available for certain bands, for some energy ranges such as above 1200 cm−1 reliable data virtually do not exist. In addition, high-level ab initio calculations are neither reported for ketenimine nor for one of its deuterated isotopologues. In this paper, we provide for the first time data from accurate quantum chemical calculations and a thorough analysis of the full rovibrational spectrum. Based on high-level potential energy surfaces obtained from explicitly correlated coupled-cluster calculations including up to 4-mode coupling terms, the (ro)vibrational spectrum of ketenimine has been studied in detail by variational calculations relying on rovibrational configuration interaction (RVCI) theory. Strong Fermi resonances were found for all isotopologues. Rovibrational infrared intensities have been obtained from dipole moment surfaces determined from the distinguishable cluster approximation. A comparison of the spectra of the CH2CNH molecule with experimental data validates our results, but also reveals new insight about the system, which shows very strong Coriolis coupling effects.

Spectroscopic Characterization of Diazophosphane—A Candidate for Astrophysical Observations

“…However, it is subject to intensity borrowing due to coupling with the much weaker overtones 2ν 5 and 2ν 6 . As discussed in Tschöpe et al (2021) and Tschöpe & Rauhut (2023), this leads to the typical compression of the branch facing the borrowing bands, i.e., toward higher energies, in this case. Another typical example of an A-type pattern arises for ν 2 , which was to be expected since it is assigned to the N≡N stretching mode.…”

“…Compared to these previous works, this effect is smaller for diazophosphane than for other molecules. This is not surprising, as the largest differences were observed for CH bond lengths (Tschöpe et al 2021;Tschöpe & Rauhut 2023), which are not present in diazophosphane. However, the largest absolute difference between r a and r g was again found for the bond involving hydrogen, i.e., Δ r(PH) = 0.008 Å.…”

“…During recent decades, various approaches avoiding the need for model Hamiltonians have been developed to investigate rotational, vibrational, and rovibrational spectra by the groups of Yachmenev et al (2011) (Yachmenev et al 2013;Yurchenko et al 2017;Clark et al 2020), Nikitin et al (2017) (Rey et al 2017;Tyuterev et al 2019), Carter et al (2012) (Carter et al 2017), Rauhut (2004) (Tschöpe et al 2021), Smydke et al (2019) (Ferenc & Matyus 2019;Tobias et al 2019;Santa Daria et al 2021), and many more (Wang & Carrington 2013;Sarka et al 2019;Simmons et al 2019). Some of these are based on the seminal work of Watson (1968), introducing the respective Hamiltonian.…”

A numerical-tensorial “hybrid” nuclear motion Hamiltonian and dipole moment operator for spectra calculation of polyatomic nonrigid molecules

“…For semirigid molecules whose PES has a single, well-defined equilibrium configuration, the use of normal coordinates within the framework of the Eckart-Watson Hamiltonian formalism 50 is well established. Recent papers 23,[51][52][53][54][55] devoted to the construction of accurate line lists for many polyatomic semirigid molecules proved how the Watson Hamiltonian was still of primary importance for the modelling of planetary atmospheres. For nonrigid "floppy" molecules exhibiting one or several large amplitude motions (LAM) connecting multiple potential wells, the use of rectilinear normal coordinates designed for small amplitude vibrations is clearly prohibited.…”

Novel methodology for systematically constructing global effective models from ab initio-based surfaces: A new insight into high-resolution molecular spectra analysis

“…As a comparison, the same number of lines up to P = 4 (tetradecad, <6200 cm −1 ) was assigned over the past 40 years. With the development of modern and efficient algorithms, combined to the constant advances in the computer technology, it is now possible to obtain approximate solutions of the Schrödinger equation for molecules with more than 5 atoms [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] and to achieve very satisfactory convergence of (ro)vibrational levels. Several research groups have followed different strategies to significantly reduce the memory cost (see e.g.…”