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A multitransition 3‐mm molecular line single pointing and mapping survey was carried out towards 29 massive star‐forming cores in order to search for the signature of inward motions. Up to seven different transitions, optically thick lines HCO + (1‐0), CS(2‐1), HNC(1‐0), HCN(1‐0) and  12 CO(1‐0), and optically thin lines C 18 O(1‐0) and  13 CO(1‐0) were observed towards each source. The normalized velocity differences () between the peak velocities of optically thick lines and optically thin line C 18 O(1‐0) for each source were derived. Prominent inward motions are probably present in either HCO + (1‐0) or CS(2‐1) or HNC(1‐0) observations in most sources. Our observations show that there is a significant difference in the incidence of blueshifted asymmetric line profiles between CS(2‐1) and HCO + (1‐0). The HCO + (1‐0) shows the highest occurrence of obvious asymmetric features, perhaps owing to different optical depth between CS(2‐1) and HCO + (1‐0). HCO + (1‐0) appears to be the best inward motion tracer. The mapping observations of multiple line transitions enable us to identify six strong infall candidates: G123.07‐6.31, W75(OH), S235N, CEP‐A, W3(OH) and NGC 7538. The infall signature is extended up to a linear scale  &gt;0.2 pc .

A multitransition molecular line study of inward motions towards massive star‐forming cores