# A rotational investigation of the three isomeric forms of cyanoethynylbenzene (HCC-C$_6$H$_4$-CN): benchmarking experiments and calculations using the ''Lego brick'' approach

### Abstract

We report the study of three structural isomers of phenylpropiolonitrile (3-phenyl-2-propynenitrile, C6H5–C3N) containing an alkyne function and a cyano group, namely ortho-, meta-, and para-cyanoethynylbenzene (HCC–C6H4–CN). The pure rotational spectra of these species have been recorded at room temperature in the millimeter-wave domain using a chirped-pulse spectrometer (75–110 GHz) and a source-frequency modulation spectrometer (140–220 GHz). Assignments of transitions in the vibrational ground state and several vibrationally excited states were supported by quantum chemical calculations using the so-called ‘‘Lego brick’’ approach [A. Melli, F. Tonolo, V. Barone and C. Puzzarini, J. Phys. Chem. A, 2021, 125, 9904–9916]. From these assignments, accurate spectroscopic (rotational and centrifugal distortion) constants have been derived: for all species and all observed vibrational states, predicted rotational constants show relative accuracy better than 0.1%, and often of the order of 0.01%, compared to the experimental values. The present work hence further validates the use of the ‘‘Lego brick’’ approach for predicting spectroscopic constants with high precision.

Publication
Phys. Chem. Chem. Phys.
##### Jean-Thibaut Spaniol
###### Master Student

Former Master 2 student with a passion for teaching that overpassed his love for spectroscopy.

##### Olivier Pirali
###### Director of Research

My research interests includes high resolution molecular spectroscopy, laboratory astrophysics, and THz generation.

##### Marie-Aline Martin-Drumel
###### Researcher

My research interests focus on molecular spectroscopy of stable molecules and reactive species, and its applications for astrophysics and physical-chemistry.