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tokens: of H 2 in the interstellar medium (Habart et al. 2005 ), several studies have attempted to gain insight into the conditions in PNe where this species is found. The correlation between the bipolar morphology of PNe and the H 2 detection is well documented (Kastner et al. 1996 ), suggesting that the H 2 -bright waists of bipolar PNe are the remnants of dense molecule-rich circumstellar discs. Alternatively, it has been claimed that the preferential detection of H 2 emission in bipolar PNe may be an effect of the typically higher effective temperature of their central stars (Phillips 2006 ; Aleman Gruenwald 2004 , 2011 ). The consensus is that the brightest H 2 emitters tend to be bipolar PNe, but deep near-IR imaging of the 2.122 μm H 2 emission line shows that this emission is not exclusive to this morphology (Marquez-Lugo et al. 2013 ). Besides the excellent near-IR spectroscopic survey of PNe and study of upper vibrational levels carried out by Hora, Latter Deutsch ( 1999 ), an actual investigation of the excitation mechanism of H 2 in PNe and calculations of its excitation temperature have been made in the context of other detailed studies (see e.g. Hora Latter 1994 , 1996 ; Shupe et al. 1998 ; Rudy et al. 2001 ; Lumsden, Puxley Hoare 2001 ; García-Hernández et al. 2002 ; Davis et al. 2003 ; Likkel et al. 2006 ; Ramos-Larios, Guerrero Miranda 2008 ; Aleman et al. 2011 , and references therein). Mid-IR spectroscopy is a powerful tool for the study of the thermal and molecular emission from PNe, since such observations are much less affected by dust extinction. Mid-IR studies of PNe have focused on imaging surveys (e.g. Hora et al. 2004 ; Phillips Ramos-Larios 2008 , 2010 ; Zhang Kwok 2009 ; Zhang, Hsia Kwok 2012 ), but mid-IR spectroscopy of PNe has only been carried out for individual objects for which chemical abundances and H 2 excitation temperatures were obtained (Cox et al. 1998 ; Matsuura Zijlstra 2005 ; Hora et al. 2006 ; Phillips, Ramos-Larios Guerrero 2011 ). Currently, mid-IR studies of the excitation temperature of H 2 in PNe are scarce. Using archival Spitzer mid-IR spectroscopy, we have conducted a spectroscopic survey of PNe to assess the presence of ionic species, polycyclic aromatic hydrocarbons (PAHs), and molecular hydrogen. The H 2 excitation temperature has been derived using its mid-IR emission lines. These temperatures shed light on the purely rotational component of the excitation temperatures to complement the rotational–vibrational studies obtained by near-IR observations. Section 2 details the criteria for target selection and data processing. Section 3 describes the mid-IR spectroscopic properties of each PN in our sample. A review of the theory behind the data analysis is given in Section 4 and the final discussion is presented in Section 5 . 2 ARCHIVAL DATA: SELECTION AND REDUCTION 2.1 The <italic>Spitzer</italic> archive This study made use of the Spitzer Space Telescope (Werner et al. 2004 ) data base. We