VMS-ROT: A New Module of the Virtual Multifrequency Spectrometer for Simulation, Interpretation, and Fitting of Rotational Spectra

Abstract

The Virtual Multifrequency Spectrometer (VMS) is a tool that aims at integrating a wide range of computational and experimental spectroscopic techniques with the final goal of disclosing the static and dynamic physical–chemical properties “hidden” in molecular spectra. VMS is composed of two parts, namely, VMS-Comp, which provides access to the latest developments in the field of computational spectroscopy, and VMS-Draw, which provides a powerful graphical user interface (GUI) for an intuitive interpretation of theoretical outcomes and a direct comparison to experiment. In the present work, we introduce VMS-ROT, a new module of VMS that has been specifically designed to deal with rotational spectroscopy. This module offers an integrated environment for the analysis of rotational spectra: from the assignment of spectral transitions to the refinement of spectroscopic parameters and the simulation of the spectrum. While bridging theoretical and experimental rotational spectroscopy, VMS-ROT is strongly integrated with quantum-chemical calculations, and it is composed of four independent, yet interacting units: (1) the computational engine for the calculation of the spectroscopic parameters that are employed as a starting point for guiding experiments and for the spectral interpretation, (2) the fitting-prediction engine for the refinement of the molecular parameters on the basis of the assigned transitions and the prediction of the rotational spectrum of the target molecule, (3) the GUI module that offers a powerful set of tools for a vis-à-vis comparison between experimental and simulated spectra, and (4) the new assignment tool for the assignment of experimental transitions in terms of quantum numbers upon comparison with the simulated ones. The implementation and the main features of VMS-ROT are presented, and the software is validated by means of selected test cases ranging from isolated molecules of different sizes to molecular complexes. VMS-ROT therefore offers an integrated environment for the analysis of the rotational spectra, with the innovative perspective of an intimate connection to quantum-chemical calculations that can be exploited at different levels of refinement, as an invaluable support and complement for experimental studies.

A twist on the reaction of the CN radical with methylamine in the interstellar medium: new hints from a state-of-the-art quantum-chemical study

“…The list of spectroscopic parameters, computed as explained above and -in more details-in the Appendix, is reported in Table 4, with the principal inertia axes being displayed in Figure 5. The spectroscopic properties of Table 4 have been employed to simulate the rotational spectra at T = 100 K using the VMS-ROT software (Licari et al 2017): the predicted rotational spectra in the 0-1000 GHz frequency range are depicted in Figure 6. According to the literature on this topic (see, e.g., Puzzarini et al (2008 (2018)), the rotational constants are expected to have an accuracy, in relative terms, of about 0.1%, while the uncertainties affecting centrifugal-distortion constants and hyperfine parameters should not exceed 1-2%.…”

Accuracy Meets Interpretability for Computational Spectroscopy by Means of Hybrid and Double-Hybrid Functionals

“…VMS features two interconnected tools: VMS-Draw (Licari et al, 2015) and VMS-Comp (Barone et al, 2012), the former providing a user-friendly, graphical user interface to pilot the latter, which is in charge of computationally intensive tasks. VMS-Comp includes a wide set of algorithms and calculation options and it allows the user to predict with remarkable accuracy many types of spectroscopic data for a vast range of molecular systems and environments (Zerbetto et al, 2013;Licari et al, 2017;Presti et al, 2017). Further developments are, however, needed to deal with new and more sophisticated experimental techniques (Quack and Merkt, 2011;Lane, 2018).…”

Prebiotic molecules in interstellar space: Rotational spectroscopy and quantum chemistry

“…The integrated experiment-theory approach employed in our laboratory is illustrated in Figure 1: state-of-the-art quantum-chemical calculations are performed in order to obtain accurate predictions of the rotational spectroscopy parameters that are subsequently used to plan the experimental measurements, to support the spectral assignment, and -if the case-to complement experiment with missing information. To exploit this interplay of experiment and theory, we rely on the VMS-ROT software (Licari et al 2017), developed in the framework of the Virtual Multi-frequency Spectrometer project (see Barone 2016). VMS-ROT is composed of four independent modules: (1) the computational one which is in charge of the quantum-chemical calculations of the spectroscopic parameters, (2) the prediction-fitting module, which makes use of Pickett SPFIT/SPCAT program (Pickett 1991) for predicting the rotational spectrum and, once the experimental spectrum is available, for assigning the recorded transitions and thus refine the starting computed constants, (3) the graphical user interface (GUI) module that offers a powerful set of tools for a vis-á-vis comparison of experimental and simulated spectra, and (4) the assignment tool for assigning the experimental transitions in terms of quantum numbers upon comparison with the predicted ones.…”