For a city to truly become a "smart city", and to narrow the digital divide, Municipalities must foster collaborative digital environments. The process of engaging with citizens in the planning and decision making processes through the use of information technology (IT) is called e-participation. Despite the increasing availability of solutions for e-participation, its adoption by citizens is still a challenge, and for many citizens, political participation means no more than voting in the elections for government. Several different technological, social, and political factors need to be taken into account by public authorities when planning, designing, and implementing e-participation initiatives. This paper extends the unified theory of acceptance and use of technology (UTAUT2) model to the e-participation context, seeking to identify the main factors that explain citizens' intention to adopt e-participation, and providing valuable insights for government institutions and developers of these citizen engagement applications. Our proposed model incorporates three constructs based on social capital theory into UTAUT2: trust in government, civic engagement, and interpersonal trust. The extended framework proposed herein provides new insights on citizens' intentions to adopt e-participation, significantly increasing the variance explained in behavioural intention. The data collected are analysed using the partial least squares equation modelling (PLS-SEM) method.