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Rotational spectroscopy (ROT) is a powerful technique that, thanks to its intrinsic high resolution and high sensitivity, allows for accurately characterizing stable and transient species (ions, radicals, neutral molecules and clusters) in the gas phase and deriving information on their molecular structures and dynamics, information that hardly accessible from other experimental techniques. However, the task of extracting the aforementioned information, which starts with inverting the spectral observables, i.e., with the assignment of rotational transitions to an effective Hamiltonian, is challenging, time-consuming, and prone to errors. The availability of different kinds of microwave spectrometers (Frequency modulated spectrometers, Chirped-pulsed Fourier Transform, Pulsed-jet Fourier Transform etc.) and different gas phase generating systems (laser ablation, electric discharge, heating systems, pyrolysis etc.) makes it possible to investigate a large variety of molecules and/or clusters, which have, among the others, chemical, biological, and astrochemical interest.

To speed up and facilitate spectral assignment procedures, quantum-chemical calculations are essential; therefore, an intimate link between theory and experiment is unavoidable. In this respect,the ** VMS-ROT module of the VMS-DRAW graphical user interface is the most suitable tool to simulate, interpret and assign a rotational spectrum, because it is actually based on the interplay of theory and experiment, also enabling the user to easily deal with different microwave techniques.**

VMS-ROT offers an integrated suite of tools for assisting the interpretation and understanding of rotational spectra: from the assignment of the spectral transitions and the refinement of spectroscopic constants to the prediction and simulation of the spectrum.

It is an complete 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.

This video describes how to simulate a rotational spectrum from calculations either directly using a Gaussian output file (*.log) or the user created .VAR and .INT files (the SPCAT input files of Pickett’s program).

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

In this video, we introduce the new assignment tool for the assignment of experimental transitions

in terms of quantum numbers upon comparison with the simulated ones.

It describes how to assign and fit a rotational spectrum once the simulation of the calculated spectrum has been already performed. The dialog panel where the fitting parameters are listed is fully described as well as the fit, save and load options

The VMS Peak Analyzer wizard offers an in-built and interactive interface to walk users through the steps of advanced peak analysis.

A Savitzky–Golay filter is a digital filter that can be applied to a set of digital data points for the purpose of smoothing the data to increase the signal-to-noise ratio without greatly distorting the signal.
A common requirement in scientific data processing is to detect peaks in a spectrum.

This video describes how to use the VMS Peak Analyzer wizard tool to:

- 1. smooth the experimental continuous spectrum (optional tool).
- 2. determine the frequency value of a transition peak directly from a continuous spectrum.

Rotational spectra recorded using a COBRA-type Pulsed-Jet Fourier-Transform Microwave (PJ-FTMW) spectrometer, show the splitting in two components of each rotational transition by Doppler effect.

Because of this, rest frequencies are obtained as the arithmetic mean of the frequencies of the two Doppler components.

The mean frequency of the two Doppler components is obtained by using manual procedures, the new VMS Doppler tool wants quickly transform costly, error-prone processes into streamlined and automated operations. This video describes how to use the Peak Analyzer tool to deal with Doppler splitting in a really powerful, user-friendly and automatic way, starting from a .XY exported continuous spectrum from a COBRA type Pulsed-Jet Fourier Transform Microwave Spectrometer.