The nature of the E center dot center dot center dot E' pnicogen bond (E = N, P, As) in dimers such as H2FP center dot center dot center dot PH2F (1) and H3N center dot center dot center dot PHNO2 (2) can be described using vibrational spectroscopy in form of the calculated infrared and depolarized Raman scattering spectra. Utilizing the six calculated intermonomer frequencies, the corresponding local mode E center dot center dot center dot E' stretching frequency and force constant are obtained, where the latter provides a unique measure of the E center dot center dot center dot E' bond strength. Pnicogen bonding in 1 is relative strong (bond strength order n = 0.151) and covalent whereas pnicogen bonding in 2 is electrostatic (n = 0.047) because of a different bonding mechanism. (C) 2014 Elsevier B.V. All rights reserved.