Research involves computational chemistry as well as (experimental) high-resolution rotational spectroscopy: state-of-the-art quantum-chemical computations of structural, energetic, molecular and spectroscopic properties as well as characterization (by means of rotational spectroscopy) of stable and unstable (radicals and ions) molecular species of astrochemical and/or atmospheric relevance. The interplay of theory and experiment is a
defining characteristic of the research activity.
High-resolution molecular spectroscopy (2000-present).
Rotational spectroscopy plays an important role in atmospheric and astrophysical investigations. In the last few decades, study of the Earth’s and planetary atmospheres as well as the interstellar medium by means of spectroscopic techniques has grown rapidly. Two principal research areas can be outlined:
- Rotational Spectroscopy for Atmospheric Studies: Remote sensing requires the
knowledge of the spectroscopic parameters of molecular species: transition frequencies and intensities, pressure- and shift-broadening coefficients, and their temperature dependence. Examples of the evaluation of these parameters by means of rotational spectroscopy are provided by Refs. [1, 2]. Spectroscopic databases collect such data and are continuously updated .
- Rotational Spectroscopy for astrochemical/physical Studies: For the identification of molecular species in space, astronomical observations require knowledge of accurate rest frequencies. In particular, gas-phase species have been detected mostly via observation of their rotational signatures, which in turn have been measured in the laboratory or directly derived from spectroscopic parameters obtained from laboratory studies [4–8]. Collisional rates and transition moments are needed in order to interpret interstellar spectra in terms of local physical conditions, with experimental estimates relying on measurements of collision-induced spectral broadening . Another important
aspect of rotational spectroscopy is the observation, if present, of the hyperfine
structure of the rotational spectra. Its omission can lead to an overestimation of the line width of molecular emission lines, thus leading to unrealistic abundances of the species under consideration [10, 11]. Determination of precise frequencies of molecular line transitions (also required for astronomical standard) as well as the observation of the hyperfine structure of rotational spectra requires in most cases sub-Doppler resolution. In the field of millimeter-/submillimeter-wave spectroscopy this can be obtained
by exploiting the Lamb-dip effect, also in the THz frequency domain (this represents a unique capability of the lab in Bologna ).
- Determination of molecular structure and chemical properties is a third research line involving the interplay of experiment and theory [13–15].
Quantum-chemical computations of structural, molecular and spectroscopic properties (1996-present).
Implementation of very accurate ab initio methods together with improvements in computational capabilities allow high accuracy determinations of structural, thermochemical, molecular, and spectroscopic properties of small- to medium-sized molecules [16, 17]. The predictive capabilities are now so good that theoretical calculations can guide, support, and even challenge experiment. To perform accurate state-of-the-art quantum-chemical calculations, highly correlated methods, such as coupled-cluster, are employed. Then, extrapolative and additive schemes account for basis set and wavefunction truncation errors as well as include important corrections, such as those related to core correlation and relativistic effects. My original contributions in this field concern the development of effective composite schemes for accurate determination of
structural, molecular, and spectroscopic properties of building-blocks of biomolecules (see, for example, Refs. [18–20]). These approaches provide structural parameters and relative stabilities with an accuracy of 0.001-0.002 Å for bond distances and 0.1 degrees for angles, and 1-2 kJ/mol for relative energies [20, 21]. Rotational transitions can be predicted with uncertainties smaller than 0.1% [22, 23], while for infrared transitions the uncertainties are as small as 5-10 cm-1. Another original contribution concerns the implementation of the computation of sextic centrifugal-distortion constants in the quantum-chemical program package CFOUR .
Astrochemistry spans astronomical observations, modelling, and laboratory based investigations . The main aim of astrochemistry is to understand the chemical evolution of the universe. Major goals are detection of molecular species and the study of the abundance and reactions of chemical elements and molecules in the universe, and their interaction with radiation.
- Molecules in space: Molecules can exist in a wide range of astrophysical environments, from the extremely cold regions between stars to the atmospheres of stars themselves. Spectroscopic signatures provide unequivocal proof of their presence. The research activity along this line exploits the expertise and skills outlined above for their application to astrochemistry, thus involving both quantum-chemical computations and spectroscopic measurements [7, 24–27].
- Formation routes in space: One goal of astrochemistry is to understand how the emergence of life occurred. Two alternative theories have been suggested so far: (1) endogenous and (2) exogenous synthesis. In the first theory (1), the synthesis of simple organic molecules having a potential relation to the origin of life occurred directly on our planet starting from simple parent molecules in the atmosphere, liquid water and various energy sources. The Urey-Miller experiment was a milestone in this theory. In the exogenous theory (2), prebiotic molecules came from space, the carriers being comets, asteroids and meteorites. The rationale behind this suggestion is that plenty of complex organic molecules have been observed in interstellar clouds. In the context
of the endogenous theory (1), Titan (the largest moon of Saturn) has been postulated to represent a model of primitive Earth. Therefore, the organic chemistry in Titan’s atmosphere is intimately linked to prebiotic organic synthesis in the atmosphere of our primitive planet [28, 29]. On the other hand, in the frame of exogenous theory (2), it is of fundamental importance not only to discover prebiotic species in space, but also to understand how they could be produced in the typical harsh conditions (extremely low temperature and density) of the ISM. Since laboratory experiments are not able to correctly reproduce these extreme conditions, accurate state-of-the-art computational
approaches are carried out to derive possible reaction mechanisms .
 G. Cazzoli, C. Puzzarini, G. Buffa, O. Tarrini, “Pressure-broadening of water lines in the THz frequency region: improvements and confirmations for spectroscopic databases. Part II.”, J. Quantitative Spectrosc. Radiat. Transfer (HITRAN special issue), 110 (2009) 609.
 G. Cazzoli, T. Kirsch, J. Gauss, C. Puzzarini, “The rotational spectrum of 17O2 up to the THz region”, J. Quantit. Spectrosc. Radiat. Transfer, 168 (2016) 10.
 A. Perrin, C. Puzzarini, J.-M. Colmont, C. Verdes, G. Wlodarczk, G. Cazzoli, S. Buehler, J.-M. Flaud, J. Demaison, “Molecular line parameters for "MASTER" (Millimeter wave Acquisitions for Stratosphere/Troposphere Exchange Research) database”, Journal of Atmospheric Chemistry, 50 (2005) 161.
 G. Cazzoli, C. Puzzarini, “Observation of OD- using microwave spectroscopy: a new candidate for astrophysical detection?”, Astrophys. J., 648 (2006), L79.
 G. Cazzoli, C. Puzzarini, S. Stopkowicz, J. Gauss, “Lamb-dip and THz spectra of monodeuterated trans-formic acid isotopologues (DCOOH, HCOOD): improvements for astrophysical detections”, Astrophys. J. Suppl. S., 196 (2011) 10.
 G. Cazzoli, L. Cludi, G. Buffa, C. Puzzarini, “Precise THz measurements of HCO+, N2H+ and CF+ for astrophysical observations”, Astrophys. J., 203 (2012) 11.
 G. Cazzoli, C. Puzzarini, J. Gauss, “Rare isotopic species of hydrogen sulfide: the rotational spectrum of H2(36)S", Astron. Astrophys., 566 (2014) A52.
 V. Lattanzi, G. Cazzoli, C. Puzzarini, “Rare isotopic species of sulphur monoxide: the rotational spectrum in the THz region”, Astrophys. J., 813 (2015) 4.
 G. Cazzoli, C. Puzzarini, “N2-, O2-, H2-, and He-broadening of SO2 rotational lines in the mm-/submm-wave and THz frequency regions: the J and Ka dependence”, J. Quantitative Spectrosc. Radiat. Transfer, 113 (2012) 1051.
 G. Cazzoli, C. Puzzarini, S. Stopkowicz, J. Gauss, “Hyperfine structure in the rotational spectrum of trans-formic acid: Lamb-dip measurements and quantum-chemical calculations”, Astron. Astrophys., 520 (2010) A64.
 G. Cazzoli, V. Lattanzi, J. L. Alonso, J. Gauss, C. Puzzarini, “The hyperfine structure of the rotational spectrum of HDO and its extension to the THz region: Accurate rest frequencies and spectroscopic parameters for astrophysical observations”, Astrophys. J., 806 (2015) 100.
 G. Cazzoli, C. Puzzarini, “Sub-Doppler resolution in the THz frequency domain: 1 kHz accuracy at 1 THz by exploiting the Lamb-dip technique.", J. Phys. Chem. A, 117 (2013) 13759.
 C. Puzzarini, G. Cazzoli, J.C. López, J.L. Alonso, A. Baldacci, A. Baldan, S. Stopkowicz, L. Cheng, J. Gauss, “Rotational spectra of rare isotopic species of fluoroiodomethane: determination of the equilibrium structure from rotational spectroscopy and quantum-chemical calculations”, J. Chem. Phys., 137 (2012) 024310.
 T. U. Helgaker, J. Gauss, G. Cazzoli, C. Puzzarini, 33S hyperfine interactions in H2S and SO2 and revision of the sulfur nuclear magnetic shielding”, J. Chem. Phys., 139 (2013) 244308.
 C. Puzzarini, G. Cazzoli, M. E. Harding, J. Vázquez, J. Gauss, “The hyperfine structure in the rotational spectra of D2(17)O and HD(17)O: Confirmation of the absolute nuclear magnetic shielding scale for oxygen", J. Chem. Phys., 142 (2015) 124308.
 C. Puzzarini, J. F. Stanton, J. Gauss, “Quantum-chemical calculation of spectroscopic parameter for rotational spectroscopy”, Int. Rev. Phys. Chem., 29 (2010) 273.
 C. Puzzarini, “Rotational spectroscopy meets theory”, Phys. Chem. Chem. Phys., 15 (2013) 6595. [invited PESPECTIVE article]
 C. Puzzarini, V. Barone, “Extending the molecular size in accurate quantum-chemical calculations: the equilibrium structure and spectroscopic properties of uracil”, Phys. Chem. Chem. Phys., 13 (2011) 7158.
 C. Puzzarini, M. Biczysko, V. Barone, “Accurate anharmonic vibrational frequencies for uracil: the performance of composite schemes and hybrid CC/DFT model”, J. Chem. Theory Comp., 7 (2011) 3702.
 V. Barone, M. Biczysko, J. Bloino, C. Puzzarini, “Accurate structure, thermodynamic and spectroscopic parameters from CC and CC/DFT schemes: the challenge of the conformational equilibrium in glycine”, Phys. Chem. Chem. Phys., 15 (2013) 10094.
 V. Barone, M. Biczysko, J. Bloino, P. Cimino, E. Penocchio, C. Puzzarini, “CC/DFT Route toward Accurate Structures and Spectroscopic Features for Observed and Elusive Conformers of Flexible Molecules: Pyruvic Acid as a Case Study”, J. Chem. Theo. Comp., 11 (2015) 4342.
 C. Puzzarini, M. Biczysko, V. Barone, M. I. Pena, C. Cabezas, J. L. Alonso, “Accurate molecular structure and spectroscopic properties for nucleobases: A combined computational - microwave investigation of 2-thiouracil as a case study.”, Phys. Chem. Chem. Phys., 15 (2013) 16965.
 C. Puzzarini, M. Biczysko, V. Barone, L. Largo, I. Pena, C. Cabezas, J. L. Alonso, “Accurate Characterization of the Peptide Linkage in the Gas Phase: A Joint Quantum-Chemical and Rotational Spectroscopy Study of the Glycine Dipeptide Analogue”, J. Phys. Chem. Lett., 5 (2014) 534.
 V. Barone, M. Biczysko, C. Puzzarini, “Quantum Chemistry Meets Spectroscopy for Astrochemistry: Increasing Complexity toward Prebiotic
Molecules”, Acc. Chem. Res., 48 (2015) 1413.
 C. Puzzarini, M. L. Senent, R. Domínguez-Gómez, M. Carvajal, M. Hochlaf, M. Mogren Al-Mogren, “Accurate spectroscopic characterization of ethyl mercaptan and dimethyl sulfide isotopologues: A route toward their astrophysical detection”, Astrophys. J., 796 (2014) 50.
 A. Bellili, R. Linguerri, M. Hochlaf, C. Puzzarini, “Accurate structural and spectroscopic characterization of prebiotic molecules: the neutral and cationic acetyl cyanide and their related species”, J. Chem. Phys., 141 (2015) 204302.
 G. Cazzoli, V. Lattanzi, T. Kirsch, J. Gauss, B. Tercero, J. Cernicharo, C. Puzzarini, “Laboratory measurements and astronomical search for the HSO radical”, Astron. Astrophys., 591 (2016) A126.
 A. Ali, E. C. Sittler Jr., D. Chornay, B. R. Rowe, C. Puzzarini, “Cyclopropenyl Cation - the Simplest Huckel?s Aromatic Molecole and its Cyclic Methyl Derivatives in Titan’s Upper Atmosphere”, Plan. Space Sci., 87 (2013) 96.
 A. Ali, E. C. Sittler Jr, D. Chornay, B. R. Rowe, C. Puzzarini, “Organic chemistry in Titan’s upper atmosphere and its astrobiological consequences: I. Views towards Cassini plasma spectrometer (CAPS) and ion neutral mass spectrometer (INMS) experiments in space”, Plan. Space Sci., 109-110 (2015) 46.
 F. Vazart, D. Calderini, C. Puzzarini, D. Skouteris, V. Barone, “State-of-the-art thermochemical and kinetic computations for astrochemical complex organic molecules: formamide formation in cold interstellar clouds as a case study”, J. Chem. Theory Comp., 12 (2016) 5385.