Context :

Aims : A large-scale survey of the Galactic center region in the 3 mm rotational transitions of SiO , HCO ^ { + } and H ^ { 13 } CO ^ { + } ( beamsize \sim 3 \aas@@fstack { \prime } 6 ) was conducted to provide an estimate of cloud conditions , heating mechanisms , chemistry , and other properties .

Methods : Using the NANTEN 4m telescope from Nagoya University , a region between -5. { { } ^ { \circ } } 75 < l < 5. { { } ^ { \circ } } 6 and -0. { { } ^ { \circ } } 68 < b < 1. { { } ^ { \circ } } 3 was mapped in the J = 1 \to 0 lines of HCO ^ { + } and H ^ { 13 } CO ^ { + } and in the J = 2 \to 1 line of SiO with a spacing of 3 \aas@@fstack { \prime } 75 ( HCO ^ { + } ) and 1 \aas@@fstack { \prime } 875 ( SiO and H ^ { 13 } CO ^ { + } ) .

Results : Velocity channel maps , longitude-velocity maps , and latitude-velocity maps are presented .
We identify 51 molecular clouds ; 33 of them belong to the Galactic center and 18 to disk gas .
We derive an average of the luminosity ratio of SiO ( J = 2 \to 1 ) / CO ( J = 1 \to 0 ) in clouds belonging to the Galactic center of 4.9 \times 10 ^ { -3 } and for disk clouds of 3.4 \times 10 ^ { -3 } .
The luminosity ratio of HCO ^ { + } ( J = 1 \to 0 ) / CO ( J = 1 \to 0 ) in the Galactic center is 3.5 \times 10 ^ { -2 } , and for disk clouds it is 1.5 \times 10 ^ { -2 } .
We can distinguish clearly between regions where the SiO or HCO ^ { + } dominate .

Conclusions :