The Critical 9365 {\AA} Diffuse Interstellar Band and C$_{60}^{+}$ Association

Abstract

The detection of interstellar C$_{60}^{+}$ has been debated for 30 years. The contested attribution of a weaker DIB at 9365 {\AA} was re-evaluated here on the basis of a Pearson correlation relative to 9577 {\AA}, which was previously tied to C$_{60}^{+}$ by diverse collaborations. An assessment of 11 sightlines revealed a high correlation amongst 9365$-$9577 {\AA} equivalent widths ($r=0.93 \pm 0.05$), after contamination from an adjacent line was mitigated using both numerical integration and Gaussian fits. In tandem with a recent separate study's high-$r$ evaluation linking 9577$-$9632 {\AA} across a sizable baseline: three interrelated DIBs matching C$_{60}^{+}$ laboratory findings were independently reaffirmed (9365, 9577, 9632 {\AA}). Yet further investigations are required to strengthen the case via two other weak DIBs disputedly linked to C$_{60}^{+}$, particularly owing to potential overlapping lines arising from an expansive chemical space (PAHs).