The rapid development of social media services has broadened the way people share emergency information during a social crisis. However, this also raised an issue of unverified and emotional rumors mongering. This paper extracted discrete emotions based on the Pleasure-Arousal-Dominance (PAD) emotional state model, and examined the differential effects of eight discrete emotions (sadness, disgust, fear, anger, gratitude, joy, surprise, like) on rumor-mongering during the COVID-19 crisis. We empirically tested the hypotheses by analyzing data collected from online citizens' engagement of rumor events on Sina Weibo. The findings show that emotions such as fear, anger, disgust, and surprise significantly affect rumor-mongering. In addition, the impact of sadness, like, joy and gratitude on rumor-mongering, is not significant. These findings contribute to a better understanding of the vital role of emotions in rumor-mongering during a social crisis.