The apparition of bright comets C/2012 F6 ( Lemmon ) and C/2014 Q2 ( Lovejoy ) in March-April 2013 and January 2015 , combined with the improved observational capabilities of submillimeter facilities , offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma .
We observed comet Lovejoy with the IRAM 30m telescope between 13 and 26 January 2015 , and with the Odin submillimeter space observatory on 29 January - 3 February 2015 .
We detected 22 molecules and several isotopologues .
The H _ { 2 } ^ { 16 } O and H _ { 2 } ^ { 18 } O production rates measured with Odin follow a periodic pattern with a period of 0.94 days and an amplitude of \sim 25 % .
The inferred isotope ratios in comet Lovejoy are ^ { 16 } O/ ^ { 18 } O= 499 \pm 24 and D/H = 1.4 \pm 0.4 \times 10 ^ { -4 } in water , ^ { 32 } S/ ^ { 34 } S = 24.7 \pm 3.5 in CS , all compatible with terrestrial values .
The ratio ^ { 12 } C/ ^ { 13 } C = 109 \pm 14 in HCN is marginally higher than terrestrial and ^ { 14 } N/ ^ { 15 } N = 145 \pm 12 in HCN is half the Earth ratio .
Several upper limits for D/H or ^ { 12 } C/ ^ { 13 } C in other molecules are reported .
From our observation of HDO in comet C/2014 Q2 ( Lovejoy ) , we report the first D/H ratio in an Oort Cloud comet that is not larger than the terrestrial value .
On the other hand , the observation of the same HDO line in the other Oort-cloud comet , C/2012 F6 ( Lemmon ) , suggests a D/H value four times higher .
Given the previous measurements of D/H in cometary water , this illustrates that a diversity in the D/H ratio and in the chemical composition , is present even within the same dynamical group of comets , suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system .