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Aims. We present new IRAM Plateau de Bure Interferometer observations of Arp220 in HCN, HCO$^{+}$, HN$^{13}$C J=1-0, C$_{2}$H N=1-0, SiO J = 2-1, HNCOJ$_{k,k'}$ = 5$_{0,4}$ - 4$_{0,4}$, CH$_{3}$CN(6-5), CS J=2-1 and 5-4 and$^{13}$CO J=1-0 and 2-1 and of NGC 6240 in HCN, HCO$^{+}$ J = 1-0 and C$_{2}$HN = 1-0. In addition, we present Atacama Large Millimeter/submillmeter Arrayscience verification observations of Arp 220 in CS J = 4-3 andCH$_{3}$CN(10-9). Various lines are used to analyse the physical conditions ofthe molecular gas including the [$^{12}$CO]/[$^{13}$CO] and[$^{12}$CO]/[C$^{18}$O] abundance ratios. These observations will be madeavailable to the public. Methods. We create brightness temperature line ratiomaps to present the different physical conditions across Arp 220 and NGC 6240.In addition, we use the radiative transfer code RADEX and a Monte Carlo MarkovChain likelihood code to model the $^{12}$CO, $^{13}$CO and C$^{18}$O lines ofArp 220 at ~2" (~700 pc) scales, where the $^{12}$CO and C$^{18}$O measurementswere obtained from literature. Results. Line ratios of optically thick linessuch as $^{12}$CO show smoothly varying ratios while the line ratios ofoptically thin lines such as $^{13}$CO show a east-west gradient across Arp220. The HCN/HCO$^{+}$ line ratio differs between Arp 220 and NGC 6240, whereArp 220 has line ratios above 2 and NGC 6240 below 1. The radiative transferanalysis solution is consistent with a warm (~40 K), moderately dense(~10$^{3.4}$ cm$^{-3}$) molecular gas component averaged over the two nuclei.We find [$^{12}$CO]/[$^{13}$CO] and [$^{12}$CO]/[C$^{18}$O] abundance ratios of~90 for both. The abundance enhancement of C$^{18}$O can be explained bystellar nucleosynthesis enrichment of the interstellar medium.

PdBI U/LIRG Survey (PULS): Dense Molecular Gas in Arp 220 and NGC 6240