As described previously, NPs were injected into vacuum via electrospray ionization (ESI), then guided by radio-frequency hexapole and quadrupole guides before entering a split-ringelectrode quadrupole trap. Trapped NPs were detected via their laser-heated thermal emission, and during kinetics measurements, heating was done using a 2 W continuous wave (cw) 532 nm diode-pumped solid state laser with its power controlled to set the desired TNP. Because the astrapped silica NPs do not absorb at 532 nm strongly enough to reach incandescence, during NP injection the trap center was irradiated by both the 532 nm laser operating at low power (~10 mW, ~0.2 mm diameter) and a 10 W quasi-cw CO2 laser (10.6 µm) operated at 5% duty factor with ~1 mm diameter at the trap center. Emission from a ~50 μm volume at the trap center was monitored during injection using a Si avalanche photodiode (APD), and the CO2 laser was automatically shut off within ~100 msec of detecting significant emission, while a valve was closed to isolate the trap vacuum system from the ESI source. Thus, the NPs were briefly pre-heated to incandescence during trapping, and subsequently the 532 nm laser was sufficient to heat the NPs. During NP injection, an AC voltage was applied to the trap electrodes with frequency (FRF) = 35 kHz and amplitude (V0) = 350 V0, and Ar was added to the trap chamber at a pressure of ~10 mTorr, typically allowing trapping of a single NP within a few minutes. The optical changes driven by the CO2 laser pre-heating are discussed below.